1. Write a function to compute the monthly payment required to pay
   off a loan in a given number of months using the following formula:
   payment = (r * loan-amount) / (1 - (1+r)^-n)
   where r is the monthly interest rate (annual rate divided by 12) and
   n is the number of monthly payments.

2. What time is it? 
   In python you need 
      import time
   time.time() returns the second after midnight 1970.
   You will need to use modulus % and integer division // to determine 
   hours and minutes.

3. Is a year a leap year?
   Years divisible by 4 are leap, but if the year is divisible by 
   100 it is not a leap year except if the year is divisible by 400.  
   Confusing? 

4. Decrypt a Caesar cypher (without knowing the cypher)