(2x-2y)/(36-3x)
So now you sub in the variable into the equation
(* means multiply in this case because x would make it more confusing)
((2*7)-(2*2))/(36-(3*7))
= (14-4)/(36-21)
= 10/15
then you can reduce the fraction to 2/3
so the answer is 2/3 or if you want to put it in a decimal, 0.67