Adding specific value to numbers in a specific range

[bmccarthy]

Hello
I'm having some problem converting a large amount of data points, around 2000, to different values
My company uses a measuring device to obtain specific thicknesses and we have to account for a variable that the device isn't able to account for.
This leaves us with a large table of data that needs to altered to fit this range.
Data that falls from 1-10 must have 3 added to it. Data ranging in 11-39 must have 6 added to them, and data that ranges over 40 must have 15 added to it.
What would be a correct macro to swap over all this data? Please help. Thank you.