Find when quantity is completed and return average

Hello,

I don't really know how to explain easily my problem easily so I've attached the excel and will describe what I'm hoping to do below.

First step: I want to find when my order quantity (C6) will be completed according to column E. In my excel, Order Quantity = 2000, so it will be completed by Day 9, as Cumulative Qty on Day 9 = 2172 (cell E17).
Second step: knowing on which day my order quantity will be completed, I want to show in G5 the average of Minutes Efficiency (column F) up to that day. In my example, the average from F8:F17 = 30%.

I don' know if it is possible to just use a formula in G5 or if a macro is needed.

Thanks a lot for any help !

Hi
Please see solution attached using two helper cells in Column A.
Tony