Satisfy, fulfill, meet, answer all can mean to measure up to a condition, a need, a claim, a hope, or a requirement.
They are seldom interchangeable, however, without loss of precision or expressiveness or without violation of idiom. Satisfy, with this meaning (compare SATISFY 1 ), is used chiefly in reference to things or to persons considered impersonally which are submitted to a test (as a condition, a requirement, or a hypothesis) and found to be such in constitution or makeup as not to fall short <there is one condition that a lyric ought to satisfy; it ought to pass the test of being read aloud —Binyon > <he will satisfy Newman’s famous definition of a gentleman as one who never inflicts pain —Montague >
Fulfill usually connotes more than adequacy or richness and fullness of measure; also what is fulfilled is not determined by something calculable but usually by something indefinite or immeasurable (as expectations, hopes, desires, or needs).
Meet implies exact agreement with the test or measure and therefore usually connotes mathematical equivalence; thus, “the new machine meets expectations” is slightly more tempered praise than “the new machine fulfills expectations”.
Answer usually implies even more moderation in praise than meet; while it does not quite imply dissatisfaction it seldom connotes complete content.