Question

Mrs. Hart, at age 65, can expect to live for 25 years. If she can invest at 8% per annum compounded monthly, how much does she need now to guarantee herself $300 every month for the next 25 years?
Present Value
= 900(1 - 1.0041666..)^-300)/.0041666...
= $153,954.05
I have calculated this, but it is wrong. Any ideas?