How can I set up this cell output in excel?

Question

Here's what I'm trying to do:

row 1 = input

row 2 = output

About the output: b-a

*input matches an x value in a separate table

*y value corresponding to that x will be "a"

*row 5 matches an x value in table

*y value corresponding to that x will be "b"

Answer 1

You explanation is not clear at all, but the fact you are talking about corresponding values in different cells leads to think vlookup might be what you're looking for.  Without understanding it better, however, that's just a guess.