Answer:
x=12
y=6
Step-by-step explanation:
Let's first start by moving x and y to one side (I prefer having both variables on the same side and the other number on the other side):
3x-y=30
-3x+7y=6
Add the equations to eliminate x
6y=36
Divide both sides by 6
y=6
3x-30=6
Add 30 to both sides
3x=36
Divide both sides by 3
x=12
(x,y)=(12,6)
