A roll-up summary field is the best way to display the sum of all closed won opportunity amounts at the account level. A roll-up summary field is a type of field that calculates a value from a set of related records, such as the sum, average, min, or max. A roll-up summary field can only be created on the master object of a master-detail relationship, and it can only calculate values from the detail object. For example, a roll-up summary field called Total Revenue could be created on the Account object, and it could calculate the sum of the Amount field from the Opportunity object, where the Stage field equals Closed Won. A custom report type is a tool that allows the user to create a report based on the relationships between a primary object and its related objects. A custom report type does not display a value at the account level, but at the report level. The opportunity related list is a component that shows the related opportunities for a specific account record. The opportunity related list does not display the sum of all closed won opportunity amounts, but only the individual amounts for each opportunity.