## Algebra 1: Common Core (15th Edition)

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. Thus, we subtract 2 on both sides of the equation to find that $-x=-7$. However, we need x to be positive, so we divide by negative one on both sides of the equation to get that x=7.