Zefi & Acacia are thinking of purchasing a house at a cost of $320,000. They have saved $80,000 as a down payment and the rest will be secured by a mortgage. The bank is offering a 25-year mortgage with a term of 5 years at a rate of 7% (APR) requiring monthly payments, at the end of each month. 

1. a) Calculate the amount of each payment.  
2. b) Calculate the monthly payments if they are made at the beginning of the month rather than the end.  
3. c) If Zefi & Acacia can only afford to pay $1,400 each month, how much would the bank allow them to borrow? (these payments are made at the end of each month).  
4. d) Assuming they secure the mortgage in part (c), how much of the 91'st mortgage payment is principal and how much is interest? 
5. e) How much interest would Zefi & Acacia pay over the life of the mortgage secured from part (c)?