Difference between two Date and Time Fields in Hours where the Date and Time are in Seperate Columns

Hi All,

I have a Webi Report that has the below Fields .

I have the actual Start Date in one Column, Actual Start Time in another Column  and the Actual End Date and Time , Trx Date and Time in the similiar manner.

What i want is the difference in hours

1. The difference bwt actual Start Date & Time and Actual End Date and Time in Hours

2. The difference bwt actual Start Date & Time and Trx Date and Trx Time in Hours

I tried to put Actual Start Dt and Actual Start Tm in one Cell and Actual End Dt & Tm in another Cell and tried to use '-' and it says invalid Data Type

([Act End Dt]+[Act End Tm])-([Act Start Dt]+[Act Start Tm]) is not working , any help guys to get me the difference ?