With an explanation please

Part 43X costs the Southern Division of Norris Corporation $35 to make direct materials are $14, direct labor is $6, variable manufacturing overhead is $11, and fixed manufacturing overhead is $4. Southern Division sells Part 43X to other companies for $40. The Northern Division of Norris Corporation can use Part 43X in one of its products. The Southern Division has enough idle capacity to produce all of the units of Part 43X that the Northern Division would require. What is the lowest transfer price at which the Southern Division should be willing to sell Part 43X to the Northern Division? O $35. $40. O $36 O $31