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This is the total of the invoice price and the freight and insurance on shipment for one entertainment center. These are not inventory carrying costs. Please see the correct answer for a complete explanation.
This answer results from failing to include the freight and insurance on shipment as an inventoriable cost in calculating the cost of capital to hold an entertainment center for one month. The freight and insurance on the shipment need to be included along with the invoice price in calculating the cost of capital, because they are "landing costs" and are inventoriable costs the same as the cost of the inventory is. So the cost of the inventory is the $380 invoice price plus $20 for freight and insurance on the shipment, which equals an inventory cost of $400 per unit. That is the amount that should be used to calculate the cost of capital to carry the inventory.
The freight and insurance on the shipment need to be included along with the invoice price in calculating the cost of capital, because they are "landing costs" and are inventoriable costs the same as the cost of the inventory is. So the cost of the inventory is the $380 invoice price plus $20 for freight and insurance on the shipment, which equals an inventory cost of $400 per unit. The cost of capital is given as 9% per year. So if an entertainment center is held for one month on average, the cost of capital to finance it is $400 × .09 ÷ 12, which equals $3.00, and that is an inventory carrying cost. Insurance on the inventory while it is in stock is $15, and that is another inventory carrying cost. The other costs are not inventory carrying costs. Therefore, the total carrying costs of inventory for one entertainment center is $3.00 cost of capital + $15.00 insurance on the unit while it is in inventory, or $18.00.
This answer results from two mistakes: (1) The cost of capital is calculated on the cost of the entertainment center only. The freight and insurance on the shipment need to be included along with the invoice price in calculating the cost of capital, because they are "landing costs" and are inventoriable costs the same as the cost of the inventory is. So the cost of the inventory is the $380 invoice price plus $20 for freight and insurance on the shipment, which equals an inventory cost of $400 per unit. That is the amount that should be used to calculate the cost of capital to carry the inventory. (2) The cost of capital is calculated as if one entertainment center were held for one full year before selling it. The problem says that on average, an entertainment center remains in inventory for one month before it is sold. The cost of capital to hold it for one month is only 1/12 the cost of capital to hold it for one year.