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 at the beginning of the week as $x_1$ and Jason's money as $x_2$. Then we have $x_1=33$ and $x_2=95$.

Let's denote Fred's money at the end of the week as $x_3$ and Jason's money as $x_4$. Then we have $x_3=x_1+16+74=x_1+90$ and $x_4=x_2$.

Thus, we have $x_3-x_1=90$ and we need to find $x_1$. We know that $x_1=33$, thus $x_3=33+90=123$.

Fred earned $90$ dollars over the weekend.