David did 47 push-ups in gym class today. David did 21 more push-ups than Zachary. How many push-ups did Zachary and David do altogether?
1) David did 47 push-ups in gym class today. 
2) David did 21 more push-ups than Zachary. 
3) How many push-ups did Zachary and David do altogether?

To solve this problem, we need to find out how many push-ups Zachary did. We can do this by subtracting 21 from 47. 

47 - 21 = 26 

So, Zachary did 26 push-ups. 

Now we need to add 26 and 47 to find out how many push-ups Zachary and David did altogether. 

26 + 47 = 73 

So, Zachary and David did 73 push-ups altogether.