Zachary did 2 push-ups in gym class today. David did 50 more push-ups than Zachary. John did 7 push-ups less than David. How many push-ups did John do?
Zachary did 2 push-ups. 
David did 50 more push-ups than Zachary. This means that David did 52 push-ups. 
John did 7 push-ups less than David. This means that John did 45 push-ups.