For Simple Interest Accounts the Interest Earned or Due Depends

Short Answer

For simple interest accounts the interest earned or due depends on the principal p, interest rate r, and the time t in years according to the formula I = prt.
Paul deposited $8400 in a savings account that pays 7.5% simple interest. How long will it take the account balance to reach $11,172.00 at this rate of interest, if no more deposits are made? (Hint: How much interest will be paid?)