I need help with these two problems. I can not get the formula to get the correct answer.

What is the present value of the following cash-flow stream if the interest rate is 4%? (Do not round intermediate calculations. Round your answer to 2 decimal places.) Year Cash Flow $270 WNP 470 370 Present valueA couple will retire in 40 years; they plan to spend about $21000 a year in retirement, which should last about 20 years. They believe that they can earn 7% interest on retirement savings. a. If they make annual payments into a savings plan, how much will they need to save each year? Assume the rst payment comes in 1 year. [Do not round intermediate calculations. Round your answer to 2 decimal places.) b. How would the answer to part {a} change if the couple also realize that in '15 years they will need to spend $571000 on their child's college education? (Do not round intermediate calculations. Round your answer to 2 decimal places.) Armual savings