Working out pick rate, work sheet attached,

[Presley1]

I am trying to do a formula within excel to find out Picking rates within a Warehouse to measure the picking team,
I know it is normally done by cases picked within a shift then divide by hours spent on the picking task
eg 1000 cases picked in 8 hour shift equates to pick rate 125 cases an hour,
Examples below Issue I have is eg, This is new position for me in a place where they never had pick rates , Working day 8.5 Hours with 45 minutes break time so actual working time 7 Hours 45 minutes

I have started a new job as Warehouse Manager and there is no benchmark in place for what the case rate an hour should be , The benchmark I could then judge by would be taking the 3 best pickers take their average and set benchmark eg at 85%-90% of their average, But I do not know how to do a formula on the picking task,
Picker A,B,C are the 3 besr pickers so how can I work out a pick rate that work's fairly considering cases to lines picked along with pallets which need to be wrapped which can take on average 3 minutes
Thanks Presley