The answer is 2,-3. Here’s why: you plug in. the -3 into the y in the equation so, 3x-3(-3)=15. So -3 times -3 is 9. So your equation should be 3x+9=15. Then you just solve for x. So take 9 away from both sides and you get 3x=6 (Because 15-9), so divide 3 from both sides, and x=2
