To isolate X you need to get rid of the -15 to do that you can add 15 on both sides of the equation resulting in 3x=54 now you need to divide both sides by 3 to get x on its own which is X=18.
-2/(a+b) Explanation: you are dividing negative two by the sum of a and b so you would put a+b in parentheses as the denominator and then put -2 as the numerator
