w campers went rowing in the morning. Some more campers went rowing in the afternoon. If a total of x campers went rowing that day How many campers went rowing in the afternoon?
First, we need to find out how many campers went rowing in the morning. We know that w campers went rowing in the morning, and we know that a total of x campers went rowing that day. This means that the number of campers who went rowing in the afternoon must be x - w. 

Therefore, the answer is: 

x - w