formulas please, not on excel ! step by step.

the reason i ask for it to be step by step us because i want yo leafn how to do it on paper.

7. The mortgage on your house is five years old. It required monthly payments of $1402, had an original term of 30 years, and had an interest rate of 10% (APR). In the intervening five years, interest rates have fallen and so you have decided to refinancethat is, you will roll over the outstanding balance into a new mortgage. The new mortgage has a 30-year term, requires monthly payments, and has an interest rate of 6 5/8% (APR). a. What monthly repayments will be required with the new loan? (Answer: $987.93) b. If you still want to pay off the mortgage in 25 years, what monthly payment should you make after you refinance? (Answer: $1,053.85) c. Suppose you are willing to continue making monthly payments of $1402. How long will it take you to pay off the mortgage after refinancing? (Answer: 170 months) d. Suppose you are willing to continue making monthly payments of $1402 and want to pay off the mortgage in 25 years. How much additional cash can you borrow today as part of the refinancing? (Answer: $50,969)