7 Gus deposits 25 into a bank account at the beginning of each 3-year period for 18 years (i.e. there is no deposit in year 18). The account credits interest at an annual effective rate of interest of i. The accumulated amount in the account after 18 years is X, which is 4 times as large as the accumulated amount in the account after 9 years (excluding the deposit made at t=9). FIND X 7 Gus deposits 25 into a bank account at the beginning of each 3-year period for 18 years (i.e. there is no deposit in year 18). The account credits interest at an annual effective rate of interest of i. The accumulated amount in the account after 18 years is X, which is 4 times as large as the accumulated amount in the account after 9 years (excluding the deposit made at t=9). FIND X