I know I'm smart but I DON'T GET IT! Sumif formula for mutpile cells over a 13 wk range

[mc21]

I work for a healthcare staffing company and I do metrics for all the recruiters. It was kind of dumped on me after our main guy that was an excel GENIOUS quit with little notice. I have been doing weekly metrics SHORT HAND with a rinky-dink calculator. I need to figure out the formula to add each recruiter's TOA(traveler's on assignment) and NWB (net weeks booked) for each week and the 12 before it, and then I divide that total by 13 to get what is called a "Rolling 13" average.

I have been going through each column to the recruiters specific TOA/NWB cell, writing it down for the current week and then the 12 before it, adding them and then dividing by 13. It is not difficult it is just so TIME CONSUMING and I know there is an easier way to do it I just can't figure it out.

If anybody knows a formula I should be using, please help!! I have been searching online for the past 2 hours but nothing gives me information for the specific formula I need. Thank you so much in advance to anyone who can give me some advice

[NeedForExcel]

Request you to attach a sample workbook with desired result..