sum of duration field in a report is in minutes . i need in hours.

Hi

I made a report where one filed is a duration type field . Trying to sum it in the report gives me a total in minutes and we need it in hours (divided by 60 ..) How can we do so ?

tried also to  make a calculated field in the record to divide by 60 but cant choose duration type filed in calculation ..

Would appreciate your help

Regards

MAYA