SumIf combination?

Hello folks,

Hoping someone can give me a hand here with the following problem. I currently have a set of data in one tab:

Column A: Vendor #
Column B: wk 1 (sales)
Column C: wk 2 (sales)
Column D: wk 3 (sales)
etc
Column xxx: wk 52 (sales)

In another tab I have a column A for planned week for each vendor # and column B for revised week. Now my task is if this planned week changes, how much sales would have been impacted.

Ie.
Vendor AAA : Planned week 5. Revised week 10. Will sum column with week 5 to week 10.

Please see attachment for reference.

I'm just trying to find the easiest solution. Any advice/feedback is appreciated.