help algebra

mmm...not sure about my solution, but here it is. 

First, let's combine all the like terms. Isolating 115, we get

$-8x+xy=115$

Now factoring out x from the left side, and isolating x, we find

$x\left(y-8\right)=115\\ x=\frac{115}{y-8}$

Now, I guess we want integers, so let's just see what y can be to make x an integer. 

115 only has 2 factors other and 1 and itself: 5 and 23. 

So x + y has 2 cases. 

First, y could be 13, and x is 23. 

The other option is for y to be 31, and x is 5. 

So we have $13+23=31+5=36$

So the answer is 36. 

Thanks! :)