Which of the following would offer the best return on investment? Assume that you buy $5,000 in stock in all three cases, and ignore interest and transaction costs in all your calculations.

a. Buy a stock at $60 without margin, and sell it a year later at $90.

b. Buy a stock at $20 with 50 percent margin, and sell it a year later at $30.

c. Buy a stock at $40 with 75 percent margin, and sell it a year later at $55.