There are a couple of different ways you could do this.
I'm going to do it with the least number of steps.
4d - 7 = 3d Subtract 4d from both sides.
4d - 4d - 7 = 3d - 4d
-7 = -d Divide both sides by negative one so that the variable will become positive.
-7/-1 = -d/-1
7 = d
