You guys are unnecessarily making a super-simple concept complex (

as i write a metric fuckton).
Just follow this uh.. flowchart.
1) Is it a "Condition" question under the MBE subject of Contracts? If yes, step 2:
2) There can only be two types of Conditions, either Express or Implied (a.k.a. as CCE or the Constructive Condition of Exchange). Identify which one it is by reading through the question.
3) Reading Comprehension is very important in general, but doubly so in K's, especially for short questions like these.
Note the language of
"Payment on Completion of ALL 3 BARNS."
"So.. is 2 barns cool, bro?" to which the immediate image smashing against your brain should be:
http://www.troll.me/images/angry-samuel ... -thumb.jpg
4) Let's go back to Step #2, is the condition express or implied? Obviously, it is an express condition, cause they tell you when you get paid, which is the issue.
5) Substantial Performance has absolutely nothing to do with Express Conditions, it is SOLELY the province of Implied Condition/CCE, ergo, substantial performance has absolutely no bearing on the situation at all.
Note: Further, this contract is not divisible (which is another trick answer choice), since the K terms explicitly state that payment will be made upon completion of ALL 3 barns, not 1 per, or $4000 upon completion of two or any variation thereof. They're trying to make you think in terms of divisible/installment K's which this isn't. You do 1 job, and I pay you once, DONEZO= 1 Contract.
The condition is
EXPRESS and therefore, promisor and promisee are bound by the
exact conditions stated in the contract, nothing else. You could have painted 2.9 barns, and promisor wouldn't have to hand over a penny under this K technically.
Remember that substantial performance only applies to IMPLIED conditions. A court of LAW won't give a shit about how UNFAIR the situation seems (that's for the EQUITY court later) if under EXPRESSLY stated conditions describing the manner and timing of which you are to perform and how you are to receive payment, you then with full knowledge of what the terms were, agreed to it. And frankly, in this question, it's not even remotely unfair. The painter's being an asshole.
From a court of law's p.o.v., they'll probably stare you down, thinking you're some kind of troll/idiot

if you think you can then ask for cash after 2 barns were painted, not the 3 you promised.
Substantial Performance is a remedy under implied conditions, because if it wasn't explicitly expressed as a condition on the K, then the courts want to give parties a break, because there could have been
miscommunication or confusion by either party.
However, if the conditions regarding the issue of the question (e.g. payment) was EXPRESSLY stated, and one party does not abide by it, then well... FUCK HIM, and that's the court's p.o.v. too
Hope this helps you to understand the distinction. "Conditions" was a pretty complex area of K's and MBE in general for me too, but once you understand the inner logic and rationale of the rules, I think it'll make more sense for you.
Also note that the answer explanation in the book (i have the book but frankly haven't done the questions since i'm using Adaptibar) immediately starts with a discussion of TIMING, who goes first, second, third, each condition triggering another condition until the completion of the K, which is what the whole "condition precedent, condition concurrent, and condition subsequent" dealio is all about.
For those who have the book, the answer explanation starts with a concept that doesn't seem to have fuck'n anything to do with this question. The author's simply stating that when the ORDER of conditions, who performs 1st, 2nd, 3rd, etc... is not EXPRESSLY stated, then the DEFAULT rule is that the performance that simply is more complex/takes longer will have to go first, with the performance that takes shorter/simpler being last. In this case, painting 3 barns is more complex/lengthier than a guy breaking out his wallet with the $$$, so since there is no express conditions on who has to perform first, the presumption/the default rule is that he performs first, then the performance by the other party of paying up goes last.
This wasn't always the case, back in Ye Olde England days, judges would get tons of cases of people suing each other for non-performance because there was no default rule made at the time, which one party blaming the other for "NOT PAYING ME FOR THE FOOKING BARNS FIRST!," to which the other party would say, "why should i pay first? I'll pay you AFTER you paint the barns you sheep fucker!"
As you can tell, TIMING, SEQUENCE, ORDER is the entirety of the CONDITIONS chapter of your outline/book.
The default rule isn't ALWAYS the case when a contrary condition is EXPRESSLY stated. Some restaurants will ask you to pay FIRST before eating the food, probably to prevent people running out. They'll put up signs or they'll tell you to pay up first you hoodie wearing bum (Express Condition).
If you can't explain what the distinction between a "condition," and a "promise/obligation" is, you may not be seeing the full picture.
I actually recently wrote a crap-ton on this very topic in another thread generically titled "Contract Questions" in response to someone (should still be in front page). Dunno if it'll help, but I would think so, if the notion of Conditions basically being all about Timing is a new concept to you. It is pretty damn confusing until you get it.
And I dunno what this other poster is talking about, "don't worry." This IS a
REAL MBE question.
It's a super simple question on what is unfortunately one of the more abstract and difficult areas of the MBE subjects, "conditions."
It's one of those, if you know what you're looking for, it's a 30 second question, if you don't know what you're looking, then you're wrong.