8x+15=7
In the statement the phrase the sum of can tell you that it is going to be an addition problem. So 8x ( eight times a number) would be added to the 15, 8x+15. Since its an addition problem the part where it says ' ... is seven', you know that it will all equal 7. So the answer would be 8x+15=7.
What I think is the answer to your question is -0.5:17, i guess. I'm not very sure if you wanted the answer this way or another way, so I just did it my way.
