I'm not sure if this is what you're asking for but here goes...
3x + y = 17
+ 4x - y = 18
———————
7x = 35
x = 5
sub x = 5 into eq. 1
3x + y = 17
(3 × 5) + y = 17
15 + y = 17
subtract 15 from both sides of the equation.
y = 2
Final Answer - ( 5 , 2 )
Hope this helped :)