You should know how to isolate variables, move the x to the right by subtracting it from both sides. You're left with 3y = 15-x
All you do now is divide by 3 to isolate y, you end up with your final answer, y = 5-x/3

armmermom2x

If u want u can assign some numbers to make the soultion correct for example x is -3 y is 6
x+3y=15
-3+18=15
15=15