A developer working on a time management application wants to make total hours for each timecard available to application user. a timecard entry has a master - detail relationship to a timecard. which approach should the developer use to accomplish this declaratively?

In order to make total hours for each timecard available to application user the developer should use the following approach: use a Roll-Up Summary field on the Timecard Object that calculates the total hours from timecard entries for that timecard. The roll-up summary fields calculate values from a set of related records, such as those in a related list and can only be defined on the master object.