[Zope] Calculate difference between time input?

How do I calculate the difference between two times I get from a from? Lets say time a = 09:45 and time b = 11:15 Then I want to calculate the difference. How do I calculate it? I'd also like to know how to get the answers in differen formats. For example caculating the input above I want to be able to get all of the following results: 1:30 (One hour and thirty minutes) 1,5 (One and a half hour) 90 (Ninety minutes) Help please :)