Predetermined Sliding Scale

Sample files often help here so people can see where the data is to located etc...

Assuming (as implied) the calculation is not marginal then in reality it's basic INDEX/MATCH (or even SUMIF with INDEX) - attached is a basic ex.

I've added a tiered/marginal approach also just in case...

edit: ignore the marginal - won't work accurately with the same bands as used for the non-marginal approach (would be 0,10,20,30)