what formula is correct?

4. In order to accumulate $15,500 at the end of eight years, Paul makes equal deposits at the end of each quarter into an account, which pays 2.1% interest compounded semiannually. The size of each semiannual payment is: 0.0105 a. $15,500 1-1.0105-16 b. $15,500 0.0105 101056 - 1 c. $15,500 0.0105 1.0105 1.01056 - 1 d. $15,500 0.0105 1.0105 1-1.0105-16