On 31 March 2013, David borrowed a sum from his best friend. He guaranteed that he would repay the money with interests at 7% p.a. on 31 March 2018. The total amount that he was made to pay his friend at that time was exactly $8,000 but he started studying at college so he couldnt afford to repay the loan. If interest continues to accrue, what is the amount David must pay on 31 March 2021 to fully pay off the loan? Select one:

a. $9,712.56

b. $13,125.69

c. $13,745.49

d. $9,800.34