I have the day numbers in A1 through I1.
I have the sample data in the next few rows, then GROUP in the 5th row.
A5
=SUM(A2:G4)*0.25
This is a seven-day sum.
Then I click on A5 once, to highlight it. In the bottom right corner is a small black box. When I hover the mouse over it, my mouse changes from that big white cross, to a thin black cross. This is the format painter.
Click down, and drag it right three rows.
This will apply the same formula style along these rows.
So in A6
=SUM(B2:H4)*0.25
and A7
=SUM(C2:I4)*0.25
See how the range is changing by one column for every column we moved it over?
This should give you exactly what you need!