10603, 10602, 13683, 10152, 198448 are all wrong.

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 % 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)