Answer:
=$B4*30*$C4+$B4*$A$13
Explanation:
(number of boxes × number of days in the month × cost per box) + (number of boxes × transport cost)
Use this accordance with cell addresses.
=$B4*30(not sure about the number of days)*$C4+$B4*$A$13
• Number of days are difference for each month, but commonly use 30 days. Question has asked to copy the formula. Therefore, you should include another column with number of days in the month or can use 30.
• $ is use for absolute cells.