Last week Fred had w dollars and Jason had x dollars. Over the weekend Fred delivered newspapers earning y dollars and washed cars earning z dollars. How much money did Fred earn over the weekend?
Let's denote the money Fred earned over the weekend by m.

m = y + z

Fred's total money after the weekend is w + m.

Plugging in for m we get that w + m = w + y + z.

Therefore, the answer (symbolic expression) is: 

w + y + z