Explanation
A validation rule can enforce process compliance by preventing users from saving records that do not meet certain criteria. In this case, a validation rule can prevent users from reverting to an earlier case status or leaving certain fields blank when specific case criteria are met

Explanation
The app builder should go to the Account object to build these new rollups. A roll-up summary field is a type of field that can aggregate numeric values from child records related to a parent record by a master-detail relationship. The app builder can create two roll-up summary fields on the Account object that count the number of open Opportunities and the number of won Opportunities related to each Account. Lightning App Builder is not a place where the app builder can build these new rollups. Lightning App Builder is a tool that allows the app builder to customize the layout and components of Lightning pages, such as record pages, home pages, or app pages. It cannot create new fields or relationships on objects. Lightning Object Creator is not a place where the app builder can build these new rollups. Lightning Object Creator is a tool that allows the app builder to create custom objects from spreadsheet data by uploading a file and mapping columns to fields. It cannot create roll-up summary fields or relationships on existing objects. Opportunity object is not a place where the app builder can build these new rollups. The Opportunity object is the child object in the relationship with the Account object, and roll-up summary fields can only be created on the parent object.

Explanation
Roll-up summary fields can only be created on master-detail relationships, and they can only calculate numeric fields, such as currency, percent, and number. Date and time fields are not supported for roll-up summary fields. Checkbox fields can be used in roll-up summary filters, but not in the field to aggregate