Lily borrowed a loan to study in a university. Now that she has graduated, she needs to repay the loan with quarterly installments for 6 years. The first payment (due after 3 months) and the second payment (due after 6 months) are both $400 and the payment increases by $30 every half-year, until it reaches $610 and becomes level. The nominal interest rate is 8% compounded quarterly. Find the amount of principal repaid in the 9th payment