David did 56 more push-ups than Zachary in gym class today. If David did 38 push-ups how many push-ups did Zachary and David do altogether?
First, we need to find out how many push-ups Zachary did. We know that David did 38 push-ups and that David did 56 more push-ups than Zachary, so we can say that Zachary did 38 - 56 push-ups, which is the same as -18 push-ups. 

Next, we need to find out how many push-ups David and Zachary did together. We know that David did 38 push-ups and that Zachary did -18 push-ups, so we can say that David and Zachary did 38 + -18 push-ups, which is the same as 38 - 18 push-ups, which is the same as 20 push-ups. 

Therefore the answer (numeric) is: 

20