formula to convert date and hours into total hours

formula to convert date and hours into total hours

I am trying to get the value of:  start date & time and the end date & time.

For example:

04/05/17 - 9:00 am  and  04/05/17 - 5:00 pm  = 8 total hours

The value I am looking for is the Total hours hired for the day....In this example, the answer is 8


I am using the Date/Time field in Zoho CRM

Please let me know if you need additional information.

Thank you ahead of time,

Jules