How to calculate exact time between two time?

Question

date_time                             reader_name                     vehicle_name

2017-04-14 00:01:00.000     RCC Entry                        TRANSDEV 502

2017-04-14 00:03:00.000     RCC Exit                          TRANSDEV 502

 

I want to know the exact time between reader_name of vehicle

 

Result like this:-

 

vehicle_name          from             to                            time

TRANSDEV 502     RCC Entry    RCC Exit               2 hours