Ben quit his job as an economics professor to become a golf professional. He gave up his salary ($40,000) and invested his retirement fund of $50,000 (which was earning 10 percent interest) in this venture. After all expenses, his net winnings (profit) were $45,000. Ben's economic profits were:____________.
a. $45,000.
b. $5,000.
c. zero.
d. $2,000.