To meet the business requirements and prevent the business logic that obtains the high value opportunities from being repeated in more than one place, the developer should take two actions: create a helper class that fetches the high value opportunities, and use custom metadata to hold the high value amount. By creating a helper class, the developer can encapsulate the logic that queries the opportunities based on the high value amount, and reuse the same class in both the trigger and the Lightning web component. By using custom metadata, the developer can store the high value amount as a configurable value that can be retrieved by the helper class, and avoid hard-coding the value in the code. This way, the developer can also easily change the value in the future without modifying the code. Calling the trigger from the Lightning web component would not work, as triggers are not meant to be invoked directly from the user interface, and would also violate the separation of concerns principle. Leaving the business logic code inside the trigger for efficiency would not work, as it would create code duplication and maintenance issues when the same logic is needed in the Lightning web component. Reference: [Custom Metadata Types], [Apex Design Patterns]

Based on the code snippets, the change that should be made to display the contacts' mailing addresses in the Lightning web component is to modify the SOQL query in the getAccountContacts method to include the MailingAddress field. This way, the Apex controller class can return the contacts' mailing addresses along with their names and phone numbers to the Lightning web component. The Lightning web component can then use the @wire annotation to get the data from the Apex method and display it in the lightning-datatable component. Adding a new method in the Apex controller class to retrieve the mailing addresses separately and modifying the Lightning web component to invoke this method would be inefficient and unnecessary, as the mailing addresses can be retrieved in the same query as the other fields. Extending the lightning-datatable component in the Lightning web component to include a column for the MailingAddress field would not work, as the data for that column would not be available from the Apex method. Modifying the SOQL query in the getAccountContacts method to include the MailingAddress field and updating the columns attribute in javascript file to add Mailing address fields would work, but it is not the optimal solution, as the columns attribute is already defined in the HTML template file and does not need to be duplicated in the javascript file. Reference: [Call Apex Methods from Lightning Web Components], [lightning-datatable]