Bob paid $30,000 plus traded in his truck that he had USED 100% for business for a new truck valued at $40,000. He will use the new truck 100& for business. He originally paid $30,000 for the old truck and had claimed $21,000 of sec 179 expenses and depreciation expenses over thew years. What is the gain on trade-in of his old truck?

a 500

b 1000

c 21,000

d. 30,000