time subtracting

Hi All,

I have 2 date time fields intime and outtime.

Now I need to subtract in time from out time to get total working time.The result should be like this.

4.10

So I am doing like this.But getting the error like A number or currency,date fieled required.

Please help

ToText({Command.out_time}, "hh:mm") -ToText({Command.in_time}, "hh:mm")