Divide based on a value of another cell
 

I am new to this forum so please forgive my ignorance. I don't even know if the heading for the question is correct.

Here is what I need to do. I am creating an insulation work order for my company. In column A I have a square footage so it is a number. In column B I will have one of about 30 different materials. All of these materials contain a different amount per bag. In column C I will have the amount of material to load. Now, how do I get column C to divide column A based on the amount of material contained in a bag of the item chosen in Column B? Very confusing I know!

I have looked into Vlookup, and match but have no clue how to proceed.

Any help would be greatly appreciated