2Y - X = 7 equation 1

Y + 2X = 1 equation 2

Mutiply the second equation by 2 to get:

2Y + 4X = 2

Minus this new equation from the first equation:

(2Y - X = 7) - (2Y +4X = 2)

The ys cancel out leaving you with:

-5x = 5

so x= 1

subsitute this back into thte second equation:

y + 2 = 1

y = -1

hope this helps