How to count the number of groups and use it in a calculation?

[minifelt]

Problem: Need to get the weekly sales average (Group 1 Sum Summary) by dividing it by the count of number of days the store is in operation (Group 3 Summary).

My report has 3 groups:
Group 1: Weekly Company Wide Sales Summary
Group 2: Sales by Facility for each Week
Group 3: Sales by Day for each Facility

The data set at the end this text is a sample of my report:
The Weekly Company Wide Sales Average should be:

Week 1 = 500/5 days
Week 2 = 700/4 days
Week 3 = 500/5 days

The number of days that a sale is reported varies. There are days when there is no sale. How do you get the maximum count of the group in group 3 and use this number to calculate the average in Group 1?

Thank you very much for your help

Week 1 Total Company Wide Sales: 500 (Group 1)
Facility 1 Total Facility Weekly Sales 300 (Group 2)
Day 1 Total Daily Sales 50 (Group 3)
Day 2 50
Day 3 50
Day 4 100
Day 5 50
Facility 2 200
Day 1 100
Day 2 100

------------------------------------------------------------
Week 2 Total Company Wide Sales: 700 (Group 1)
Facility 1 Total Weekly Sales 400 (Group 2)
Day 1 Total Daily Sales 100 (Group 3)
Day 2 100
Day 3 100
Day 4 100
Facility 2 300
Day 1 150
Day 2 150

-------------------------------------------------------------
Week 3 Total Company Wide Sales: 500 (Group 1)
Facility 1 Tot. Facility Weekly Sales 300 (Group 2)
Day 1 Tot. Daily Sales 50 (Group 3)
Day 2 50
Day 3 50
Day 4 100
Day 5 50
Facility 2 200
Day 1 100
Day 2 100