When a user edits the Postal Code on an Account, a custom Account text field named "Timezone" must be update based on the values in a PostalCodeToTimezone__c custom object. How should a developer implement this feature?

A developer must provide a custom user interface when users edit a Contact. Users must be able to use the interface in Salesforce Classic and Lightning Experience.
What should the developer do to provide the custom user interface?

While writing an Apex class, a developer wants to make sure that all functionality being developed is handled as specified by the requirements.
Which approach should the developer use to be sure that the Apex class is working according to specifications?

The Account object has a custom formula field,Level__c, that is defined as a Formula(Number) with two decimal places. Which three are valid assignments? Choose 3.

A developer has a VF page and custom controller to save Account records. The developer wants to display any validation rule violation to the user. How can the developer make sure that validation rule violations are displayed?