Working out the difference between two columns

Morning,

Having a few problems, I'm trying to work out the difference between two columns, so usually I would use:

=A2-B2

However the values in these columns range from:
N
B
3
4
5
6
7
8
EP

The value for N needs to be 4 and the value for B needs to be 2, and EP needs to be 9

Any ideas how I can do this?

Thanks for any help you can give

Hi,

You can use the replace function.
Find N and replace with 4

Go to Edit >> Click on Replace>>Type N in Find What >> Type 3 in Replace With.

Shortcut key is Ctrl+H

please check the attached file.