How to use Vlookup to retrieve and sum up multiple values in a table.

http://ift.tt/1Dmf7Es

As you can see here, I need a formula that uses the supplier ID in the bottom table and checks for matching supplier IDs in the top table. Then sum up the (Quantity per re-order)*(unit price) IF the "amount in stock" <= "Re-Order level"

I'm super stressed out about this and would really appreciate some help in this area.

Thanks a lot