Calculate difference in time for different fields, then sum and average time for particular field

[vij]

Hi All,

I have the following values
Alarm-----Initial Time----Acknowledge Time-----Final Response Time
A1:A10---B1: B10--------C1:C10-----------------D1:D10
EDr------11:05:19-------11:08:15----------------11:20:01
EDr------11:10:29-------11:11:15----------------11:15:01
EDr------11:25:19-------11:27:15----------------11:33:01
FA------15:05:19-------15:08:15----------------15:12:01
FA------17:05:19-------17:08:15----------------18:02:01
FA------23:05:19-------23:55:15----------------23:59:59
FA------23:55:19-------23:58:15----------------00:02:01

I want to calculate the following:

1. Time difference between D1-B1 for EDR
2. Sum of time difference for (D1:D3-B1:B3) and then average time for EDR
3. Same details for FA

Please help

 

[vij]

 

[vij]

Any suggestions would be welcome....