Perhaps I'm not even phrasing the question correctly. I am arguably loathsome at math.

Given two ranges:

A B
1000 500
2000 1000
3000 1500

If I have a variable that gives me 1750 and I want to reference that to column A... How can I get the difference calculated from column B?

Example: 1750 finds the part of the A1:A3 range in which it fits (A1:A2), then applies its own difference between the two (75%) to the B1:B2 for an answer of 875.

Of course, IRL column A is not comprised of even thousands.

I hope that is clear enough. Thank you for your time.

Cheers