David did w push-ups in gym class today. David did x more push-ups than Zachary. 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 w push-ups, and we know that David did x more push-ups than Zachary. This means that Zachary must have done w - x push-ups. 

Now, we need to find out how many push-ups Zachary and David did altogether. To do this, we need to add the number of push-ups that Zachary did to the number of push-ups that David did. We know that David did w push-ups, and we know that Zachary did w - x push-ups. This means that Zachary and David must have done w + (w - x) push-ups altogether. 

This can be simplified to 2w - x push-ups. 

Therefore, the answer (symbolic expression) is: 

2w - x