Sara opens a brokerage account and purchases 400 shares of Tesla at $20 per share. She borrows $3,000 from her broker to help pay for the purchase. The interest rate on the loan is 8% per year. If the share price moves to $18 a year from now, what is her investment return? a) -5.2% b) -20.8% c) -10% d) 20.8%