A payment was made two years ago for an amount of $36,000 to initially payoff a debt of $42,000 made four years ago. If the borrower plans to pay the remaining balance and interest accumulated next year, determine the total amount he need to pay if the interest applied is 10% compounded semi-annually.

1. $18,970.45

2. $21,673.23

3. $19,100.15

4. $20,170.13