y - x = -13
-4x + 3y = -51
Use any of the equation to find the value of x or y. In this case, I'll use the 1st equation to find the value of y.
y - x = -13
y = x - 13
Substitute the value of y in the 2nd equation to find the value of x.
-14x + 3y = -51
-14x + 3(x-13) = -51
-14x + 3x - 39 = -51
-11x = -51 + 39
-11x = -12
x = 12/11 or 1 1/11
Substitute the value of x in any equation to find the value of y.
y = x - 13
y = 12/11 - 13
y = 12/11 - (13*11/11) *to get the common denominator
y = (12 - 143)/11 = -131/11 = 11 10/11
to check: x = 12/11 or 1 1/11 ; y = -131/11 or 11 10/11
y - x = -13
-131/11 - 12/11 = -13
(-131 - 12)/11 = -13
-143/11 = -13
-13 = -13