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I know that consideration is needed to render a promise enforceable (or P.E./M.B.), but what distinguishes the two when reading a hypothetical?

For Example, Bill offers Ryan $100 to mow his lawn, which Bill accepts. Bill's promise is to give Ryan the $100, but isn't paying the $100 his consideration as well? (and vice versa for Ryan's performance.)

I'm having some serious confusion,

Thanks.