Answer is x = 7
if u plug in 7 in the second expression, we can get 7 - y = 4, isolate y and then we get 3.
Now, plug in 7 in the first equation to get 2(7) + y = 17. that results to 14 + y = 17. isolate y again and then thats also 3.
so:
x = 7
y = 3