Birch Company manufactures a part for its production cycle. The costs per unit for 5,000 units of the part are as follows: Direct materials Direct labor Variable factory overhead Fixed factory overhead Total costs $6.00 8.00 2.00 3.00 $19.00 If Birch buys this part from another company, it would save $2 per unit of fixed factory overhead costs. Spalding Company has offered to sell 5,000 units of the same part to Birch Company for $15 per unit. Assuming no other use for the facilities, Birch Company should OA) buy the part from Spalding Company to save $3 per unit B) buy the part from Spalding Company to save $1 per unit C) make the part to save $1 per unit D) buy the part to save $4 per unit