## 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 7 on both sides to get $-y=-3$. However, we need y to be positive, so we divide by negative 1 to obtain that y=3.