You must have an answer to this in the same book in which you found the question, and so ask about whatever it is in the answer that you are not clear about and I will explain.
(If you have been given this as a test then we certainly do not do your homework for you, but if you type out your suggestions then I will tell you whether or not you are correct 🙂 )
I assume, obviously, that you have watched my free lectures on relevant costing in general.