Yes, haruspex, because the truck didn't rotate, sum of counterclockwise moments (front wheels) equals to clockwise moment (at rear wheels). So I have M'1 = M'2 written above.
If I choose an axis with positive direction from left to right, then ∑M = 0 ⇔ (W'/2).d - w.2d - (W/2).d, which is the...