Please dont use excel.

Suppose that a particular emissions reduction strategy will save $25 billion each year in equivalent environmental damages. It is estimated that the strategy will produce these benefits for an expected duration of 50 years. (a) If the interest rate is 5% (i = 0.05), what is the maximum amount that will be justified to pay for this strategy? (Yani: What is the Present Value of the expected benefits?). (b) How would your answer to part (a) would change if the interest rate was instead 2% (i = 0.02)? Comment on the effect of interest rates on cost-benefit analyis