I have 2 spreadsheets. Each has an inventory number, a security
number and the second sheet has a duration. Each set of inventory
number and security number are on the same row of the spreadsheet.
The sheets don't match each other, though.

I'm struggling with how to create either an if/then or a vlookup
formula in which I say:

If (inventory number = inventory number) and (security number =
security number), then populate duration in a new cell. I've got an
if/then to work but it obviously relies on the pairs being on the same
row of both spreadsheet. I'm stuck with how to incorporate both
criteria into a vlookup formula.

Thanks for any help you can provide.