Need some assistance with this problem if possible. I am confused.

APPLY THE CONCEPTS: Determining benets of negotiated transfer price Assume that Selling Division and Buying Division are both owned by Overall Corporation. Selling Division sells a product that is used by Buying Division and outside customers. Selling Division has 18,000 units of excess capacity. Selling Division currently sells the product for $60 per unit and Buying Division currently buys 18,000 units of the product from an outside source for $60 per unit. Variable costs of the product are $12, of which $3 is the cost of selling the product to an outside customer. Using Selfing' priceless avoidable costs as the minimum price, ll in the following formula for the desired transfer price: $: