I am trying to create a weighted average based on multiple conditions
in a spreadsheet and can't quite seem to get the formula right. For
Example, my data is as follows

Client Region Year Sales Hourly Rate
Client 1 North 2008 1000000 85
Client 2 South 2008 1500000 90
Client 3 East 2007 300000 110
Client 4 North 2007 500000 105
Client 5 East 2006 3500000 98
Client 6 West 2006 150000 100
Client 7 North 2008 5000000 107
Client 8 South 2007 200000 100

From this data, I would like to calculate the weighted average hourly
rate for sales in each region for each year. So in a particular cell
I would want the weighted average of hours for customers in the north
region for 2008 which would end up being clients 1 and 7. I have
previously used sumproduct() for weighted averages, but never with
criteria, especially 2 different ones and I can't quite seem to get it
to work.