We can solve the equation system using elimination and subtitution method.
First, eliminate x to find the value of y
x - 2y = 9
x - y = 11
---------------- - (substract)
-y = -2
y = 2
The value of y is 2
Second, subtitute 2 as y in one of the equation
x - y = 11
x - 2 = 11
x = 11 + 2
x = 13
The solution
x, y = 13, 2
