Julia W. answered 03/29/13
Algebra I Made Better
In Algebra, to undo an operation you perform the opposite operation.
and, remember--whatever you do to one side, you must do to the other side--
Thus you solve your equation--
3=3y-15
3+15=3y-15+15
18=3y
since you want y by itself, you undo the multiplication by 3
divide both sides by 3
so--
18/3=3y/3
6=y