9x-2y=25 4x-5y=7

9x - 2y = 25     ...(1)

4x - 5y = 7      ...(2)

 

Multiply (1) by 5 and (2) by 2

45x - 10y = 125     ...(3)

8x - 10y = 14        ...(4)

Now both equations have the same number of y's so we simply subtract (4) from (3) term by term:

 

37x = 111

x = 111/37 = 3

Substitute this back into (2)

4*3 - 5*y = 7

12 - 5y = 7

Subtract 12 from both sides

-5y = -5

so y = 1