Kathryn deposits 160 into an account at the beginning of each 3-year period for 30 years. The account credits interest at an annual effective interest rate of i. The accumulated amount in the account at the end of 30 years is X, which is 4 times the accumulated amount in the account at the end of 15 years. Calculate X 6,257 6,489 7,434 7,880 O 8,517