How to use IF and CAST function in COGNOS?

IF [Business Unit] = 'Air Export' then '1' ELSE [Business Unit] END

A Business Unit comprises of - Air Export - Air Import - Sea Export - Sea Import

My objective is to portray the transit target days for Air Export only which is always 1 day.

Currently, I'm doing for a data item called "Transit Target 1".

There will be a data item called "Total Transit Target" which comprises of "Transit Target 1","Transit Target 2" and "Transit Target 3".

I would like to cast '1' as a float for me to do a calculation for "Total Transit Target" later on.

How do I go about doing this? Please help.