I want to calculate business hours between two dates , how we will calculate it by apex code ,(business hours standard object)

Insufficient Privileges You do not have the level of access necessary to perform the operation you requested. Please contact the owner of the record or your administrator if access is necessary.

Didn't understand relationship 'Merchandise__r' in field path. If you are attempting to use a custom relationship, be sure to append the '__r' after the custom relationship name. Please reference your WSDL or the describe call for the appropriate names.

Insufficient Privileges You do not have the level of access necessary to perform the operation you requested. Please contact the owner of the record or your administrator if access is necessary.

Didn't understand relationship 'Merchandise__r' in field path. If you are attempting to use a custom relationship, be sure to append the '__r' after the custom relationship name. Please reference your WSDL or the describe call for the appropriate names.