Zachary did 51 push-ups in gym class today. David did 22 more push-ups than Zachary. John did 4 push-ups less than David. How many push-ups did John do?
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Zachary did 51 push-ups.

David did 22 more push-ups than Zachary.

John did 4 push-ups less than David.

That means that John did 18 push-ups.