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

-5p+80=8p-50
80=5p+8p-50
80=13p-50
80+50=13p
130=13p (to get 120=12p at this step, you can multiply both sides by 12/13, but it's not necessary to arrive at the final answer)
p=10
