3x+2x=-15
5x=-15
5x/5 = -15/5
x=-3
Numbers with the same variable can be combined, which would make you add 3x and 2x to give you 5x. then to get rid of the 5 in front of the x, divide BOTH sides by 5, the 5 is then divided out from the x, and -15 divided by three is -3