quick basic math equation question I've got a solution to a economy class calculation, but I can't figure out how they came to the answer. Could you help me?
-5p + 80 = 8p +-50
.......? = ......? 
120 = 12p
p = 10
Extra: do you know which rule they are using to get from the first line to the 3d?
Many thx
Math beginner,
Frank

Add $5p+50$ to both sides of the = sign, and then simplify each side.
(If you wish you can do this in two steps: Add $5p$ and then 50 to each side of the equality sign.)
EDIT: 
The above leads to the equation $130 = 13p$ which can be solved directly by dividing both sides of the equality sign by 13: $130/13 = 13p/13$, which after simplification gives us
$10=p$ -- which is the same as saying $p=10$. 
Note: To reach the equation $120=12p$, that is contained in the original question, is not necessary in order to solve the equation.
