#### Answer

x=23

#### Work Step by Step

In order to solve this algebraic expression, we must isolate the variable. A variable is the letter in the problem (for instance, in the equation x+2=10, x is the variable). Because addition and subtraction are inverse operations (they cancel each other out), we know we must add when a number is being subtracted from the variable and subtract when a number is being added to the variable.
In the equation -8+x=15, we must get rid of the -8, which is on the same side as x, in order to solve. Thus, we add 8 to both sides of the equation to find that x=23. We plug 23 in for x and confirm that our answer is correct.