Weighted Average Formula Population

Hi,

See attached picture. This shows Profit and Growth for the stores in each region.

The percentage total is weighted based on the profit of each store in the region.

What I have is an excel sheet with hundreds of regions (going down), all with a different amount of stores. I need a way to populate each of its Region % Total with the weighted average formula (in my example, cells C8, C12, and C20) while also varying the formula to include only the stores in the region.

For example, C8 calculates the weighted average for %s in rows 2 through 7 (6 stores), but C12 calculates it for rows 9 through 11 (3 stores). I need the formula to vary based on the number of stores.

Can anyone help? Thanks.