Last week Fred had 33 dollars and Jason had 95 dollars. Over the weekend Fred delivered newspapers earning 16 dollars and washed cars earning 74 dollars. How much money did Fred earn over the weekend?
Let's denote Fred's money before the weekend by Fb, Jason's money before the weekend by Jb, Fred's money after the weekend by Fa, and Jason's money after the weekend by Ja. 

Then we have the following information: 

Fb=33, Jb=95, Fa=? , Ja=? 

Fa=Fb+16+74=33+16+74=123

Ja=Jb+95-123=95+95-123=168