Lookup tables

I have a 2 columns in a lookup table. The first of which has then been scaled over a larger number of rows (from 22 to 512) to form a new lookup table. My question is how do i linearly interpolate using the scaledup column with the unscaled 2nd column. This interpolation will then become the 2nd column in the new scaledup lookup table.
i.e.
1 3
2 6
3 9
4 12
to
1
1.5
2
2.5
3
etc...

What you are asking not clea to me. If you could provide an example of what you want the final 2 columns to look like it would be helpful.