The "100 whiteboards" doesn't really factor into the answer, since your teacher wants the final revenue per whiteboard. We could change the 100 to any number we wanted, and the final answer below would still come out the same.
Each whiteboard is initially $3.85
Tack on the 6% shipping and the cost is now 1.06*3.85 = 4.081 = 4.08 dollars per board.
Then take 175% of this to get 1.75*4.08 = 7.14