A gradient series is deposited for 15 years in an interest bearing account. The first deposit is $15,000, the annual gradient factor is $1,000. At the end of the 16th year, withdrawals from the account begin with a first sum of $50,000. The withdrawals are scheduled to continue for 20 years at a geometric factor of 8%. Calculate the necessary interest rate in the account to allow the gradient series deposits to fund the geometric series of withdrawals.