David did 30 more push-ups than Zachary in gym class today. If David did 37 push-ups how many push-ups did Zachary do?
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David did 30 more push-ups than Zachary.

That means that if we start with the number of push-ups that Zachary did, and then add 30, we'll get the number of push-ups that David did.

So, if we start with Z, which stands for the number of push-ups that Zachary did, we have:

Z + 30 = 37

That means that Zachary did 7 push-ups.