Changing the data type of a field used in an apex class from number to text will require the app builder to perform additional steps in order to retain existing functionalities. This is because changing the data type of a field may affect the apex code that references or manipulates the field value, and may cause compilation errors or unexpected results. The app builder will need to update the apex code to handle the new data type and ensure that the logic and calculations are still correct. Option B is incorrect because changing the data type of a field used in a report from a text to an encrypted field will not require additional steps, as encrypted fields can still be used in reports with some limitations. Option C is incorrect because changing the data type of a field used as an external id from number to text will not require additional steps, as external id fields can be either number or text. Option D is incorrect because changing the data type of a field used in lead conversion from number to text will not require additional steps, as lead conversion fields can be mapped regardless of their data types.

Users will be unable to view the Account Interest records or the Interest records because they do not have read access to the Interest object. This is a standard behavior of Salesforce when a user does not have access to a related object.

Roll-up summary fields can be used to count the number of related open cases for an account, including those from parent accounts if the relationship allows roll-up summaries.
Reference:
[Salesforce Help - Roll-up Summary Fields](https://help.salesforce.com/s/articleView?id=sf.fields_about_roll_up up_summary_fields.htm&type=5)

The record will not save and the validation rule's error message will be displayed because the field update will violate the validation rule. The validation rule will prevent the record from being saved if the Industry field is longer than 6 characters, and Technology is 10 characters long.

An external ID field can be a number field or a text field, but not a URL field or a phone field. A URL field is used to store web addresses and a phone field is used to store phone numbers. An external ID field is used to store unique identifiers from an external system and it can be used for upsert operations