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.

Reference:
Salesforce Help - External ID Fields

The app builder should use the CASESAFEID(Id) formula to create this new field. The CASESAFEID function returns the 18-digit case-insensitive version of the record ID, which is unique for each record in Salesforce. The 18-digit record ID is useful for exporting data to external systems that require case-sensitive IDs1. Option A, C, and D are not formulas that can return the 18-digit record ID.

Set up a delegated approver for the manager is the recommended solution to ensure all of the appropriate deals are reviewed and the leaderboard is up to date. According to the Salesforce documentation, "A delegated approver can approve records that are submitted for approval by users below them in the role hierarchy." Forwarding the approval request to the manager's assistant, having the manager log on and reassign the approval request, and using Process Builder to assign a delegated approver are not valid or feasible options.

Customers who are invited to Chatter groups can only interact with members of their groups. They cannot invite other members, @mention accounts, or request access to public groups