All you have to do is isolate m. We have to move all terms except m to the other side.
15 + 5m = 415
We have to cancel out the numbers. 15 is being added so we subtract it from both sides.
15 - 15 + 5m = 415 - 15
5m = 400
5 is being multiplied so we divide it on both sides.
5m/5 = 400/5
m = 80
We can plug in to prove.
15 + 5(80) = 415
15 + 400 = 415
415 = 415
