In this case you would set it up as

(180 represents the degree of the triangle)
Add up like terms

Subtract 130 to the other side (180-130)

Divide 10 to the other side ( 50/10)
.

Hope this was clear :)
(2x - y = -2)2
5x - 2y = -7
4x - 2y = -4
Subtract both
x = -3
5(-3) - 2y = -7
-15 - 2y = -7
-2y = 8, y = -4
Solution: (-3,-4)
Need more information on it to solve