I am working w/ a table. Lets say 25 rows/3 columns

Col 1 is product name
Col 2 is region name
Col 3 is number of units sold

I would like to get the average number of units for the sum of the products.
So if there are 2 products in the US that sold a combined 15 units, the
average would be 7.5.

I would like to do this for each region.

Please advise on formula. Thanks.