Calculate time difference in minutes in SQL Server

Question

I require the minutes-based time difference between the two times. The start time and end time I have are as follows:

start time | End Time    
11:15:00   | 13:15:00    
10:45:00   | 18:59:00

I require the first row's output to be 45, 60, 15, which represents the interval between 11:15 and 12:00, 12:00 and 13:00, and 13:00 and 13:15, respectively, in time. Can someone please help me with this?