c$.$ You lend the money to a friend who's starting a business, and she writes a contract guaranteeing you

$15\%$ simple interest return on your investment, to be paid in full at the end of $5$ years, with an option to

reinvest if the company is successful. If the company is not successful you don't get any money including

the principal amount. Note, $15\%$ of the investment is the total percent for all $5$ years, which means $3\%$

per year.