This is a fraction question obviously. The best trick not to make a mistake is to make a drawing.
You are told that you have 3" bolt with 1/4" head. It leaves 2 3/4" of "real bolt".
It goes through 1 1/2" of pine board, a 1/16" washer, and a 1/8" nut.
Common denominator is the key.
You substract to find
I may have made a mistake so I suggest you redo the calculations.
Don't hesitate to ask further questions.