A written explanation would be helpful, none of the other answers I can find are correct.

Hint: Outstanding Balance at 20 = (0.59774)*L = L - Value of first 20 payments at time 20

Question 4 A loan of L is taken over ten years and will be repaid using the sinking fund method with equal size quarterly payments (i.e. end of quarter) each of size 387.57 at a nominal annual interest rate of q% compounded quarterly. The outstanding balance for this loan after the 20th payment is 0.59774L. Calculate L. Give your answer rounded to the nearest whole number (i.e. X)