The formula for an account that earns simple interest is Pt = P0 + (P0 ⋅ r)t, where Pt represents the balance in the account after t years, P0 represents the initial deposit, and r represents the interest rate. Paul deposited $500 into an account that earned 4% simple interest annually. How much was in his account after 1 year? a. $20 b. $480 c. $520 d. $540