The two tools that an app builder could combine to display the number of open cases on the account page are Flow and Process Builder. Flow is a tool that allows the app builder to create a declarative automation that can query, manipulate, and display data from multiple objects. Process Builder is a tool that allows the app builder to create a trigger-based automation that can invoke a Flow when a record is created or updated. By using these two tools, the app builder can create a solution that can query the number of open cases for the account and parent account and display them on the account page using a screen element. Workflow is not a suitable tool, as it cannot query or display data from multiple objects. It can only perform actions such as field updates, email alerts, tasks, or outbound messages. Approval Process is not a suitable tool, as it is used to automate the approval of records based on certain criteria and predefined steps. It cannot query or display data from multiple objects.