please i want to compute unit cost of box

If you bought 3 gallons of milk and paid a total of $10.50, how would you figure out what that was for each gallon?

People seem to understand stuff better when I put it in terms of everyday things like food, but the concepts carry into every subject because the math behind it is the same. So think of it the same way. If you know many boxes you have and what the total cost of all of them were, then how do you the cost of one box?

If you're having trouble putting together the total costs, you'll have to ask a more specific question about that. (And include any work you've attempted.)