Could you explain the relationship between opportunity cost, outlay cost and purchase cost? How to get operating advantage of purchasing the goods based on them? Here is an example question and I already got the answer but don't know the reason of the answer.

Soft Cushion Company is highly decentralized. Each division is empowered to make its own sales decisions. The Assembly Division can purchase stuffing, a key component, from the Production Division or from external suppliers. The Production Division has been the major supplier of stuffing in recent years. The Assembly Division has announced that two external suppliers will be used to purchase the stuffing at $20 per pound for the next year. The Production Division recently increased its unit price to $40. The manager of the Production Division presented the following information variable cost $32 and fixed cost $8 to top management in order to attempt to force the Assembly Division to purchase the stuffing internally. The Assembly Division purchases 20,000 pounds of stuffing per month.

What would be the monthly operating advantage (disadvantage) of purchasing the goods internally, assuming the external supplier increased its price to $50 per pound and the Production Division is able to utilize the facilities for other operations, resulting in a monthly cash-operating savings of $30 per pound?

A) $1,000,000

B) $360,000

C) $(240,000)

D) $(400,000)