1. **State the problem:** Mary borrows 1500 for 4 years at 21% simple interest and agrees to make annual payments of the interest only. We need to find how much each payment is. 2. **Formula for simple interest:** $$I = P \times r \times t$$ where $I$ is the interest, $P$ is the principal, $r$ is the annual interest rate (in decimal), and $t$ is the time in years. 3. **Calculate total interest for 4 years:** $$I = 1500 \times 0.21 \times 4 = 1500 \times 0.84 = 1260$$ 4. **Since Mary pays interest annually only, each payment is the interest for one year:** Annual interest payment = $$1500 \times 0.21 = 315$$ 5. **Answer:** Each annual payment Mary makes is 315.