(1) 3x + 12y = 25
(2) 3x + 7y = 10
Subtract 12y from both sides of equation (1):
(1) 3x = 25 - 12y
You can then substitute this equation into equation (2):
(25 - 12y) + 7y = 10
25 - 5y = 10
-5y = -15
y = (-15)/(-5)
y = 3
You can then put this value into equation (1) to find the solution of x:
3x + (12 x 3) = 25
3x + 36 = 25
3x = -11
x = -11/3
So the solution of the equation is (-11/3, 3)