Your friend is celebrating her 35th birthday today and wants to start saving for her anticipated retirement at age 65. She wants to be able to withdraw $80,000 from her savings account on each birthday for 15 years following her retirement; the first withdrawal will be on her 66th birthday. Your friend intends to invest her money in the local credit union, which offers 9 percent interest per year. She wants to make equal annual payments on each birthday into the account established at the credit union for her retirement fund. a. If she starts making deposits on her 36th birthday and continues to make deposits until she is 65 (the last deposit being on her 65th birthday), what amount must she deposit annually to reach her goal? b. Suppose your friend has just inherited a large sum of money. Rather than making equal annual payments, she has decided to make one lump-sum payment on her 35th birthday to cover her retirement needs. What amount does she have to deposit? c. Suppose your friends employer will contribute $1,500 to the account every year as part of the companys profit-sharing plan. In addition, your friend expects a $30,000 distribution from a family trust fund on her 55th birthday, which she will also put into the retirement account. What annual amount must she deposit now to reach her goal?

My professor got the following answers:

A: 4,730.88 B: 48,603.46 C: 2,709.85

Please help me understand with the proper formula and step by step solution! Thank you!