Question 61103
Plug-in the value to see:
8 – x = 7 
Let x=15
So, 8-(15)= -7
so, 15 is not a solution because when you substitute 15 for x, the answer is -7, not 7.
The correct solution is:
8-x=7 [solve for x]
-x=7-8
-x=-1
So, x=1 is the solution.