you can multiply the second equation by -2
-5x + y = 15 everything by -2
10x - 2y = -30
now you can solve them
2x + 2y = -6
10x - 2y = -30
y cancels
2x= -6
10x = -30
12x = -36
/12. /12
x = -3
now to solve for y you substitute x for -3
-5(-3) + y = 15
15 + y = 15
-15 -15
y= 0
