b$.$ Compare the costs to a level plan that uses inventory to absorb fluctuations. Inventory carrying cost is $$4$ per engine per month.

Backlog cost is $$135$ per engine per month. There should not be a backlog in the last month. Set regular production equal to the

monthly average of total forecasted demand. Assume that using overtime is not an option. $($Negative amounts should be indicated by

a minus sign. Leave no cells blank $-$ be certain to enter $"0"$ wherever required. Round average inventory row, Inventory cost row,

and Total row values to $1$ decimal.$)$