Let's start with deleting +3d and -3d (because they have opposite signs)
8d-8 = 3d
Move unknown term (3d) to the left of equal with changed sign and known term (-8) to the right of equal with chenged sign.
8d-3d = 8
5d = 8
Divide both for 5
5d/5 = 8/5
d = 8/5
