desimal numbers calculation

[Esa Kivelä]

Greetings

Some newbie question:

I tried to calculate desimal numbers in RR but how can code some calculation. 
 
In the card I have some text filed where users put some numbers like 0,5, 3,4 and so on. 
 
In some field I'd like to show those fields result as ie. 0,5 + 3,4 and so on but that + operator in the script won't calculate desimal numbers. 
 
Is there any other way to sum those desimal numbers? 
 
Yours 
 
EsaK