Originally Posted by

**HallsofIvy** The first step in know **what** to do is understanding **why** you would want to do it! You object is to eliminate one of the unknown letters. You should see that the coefficient of "f" in both equations is "7". Subtracting will give 7f- 7f= 0 which eliminates "f". Adding them would not.

For 5m- p= 7, 7m- p= 11, p has coefficient -11 in both equations. Subtracting will give -11p- (-11p)= 0.

Notice that skoker multiplied an equation by -1 and **then** added. Of course, that is the same as subtracting the equations.