Application Events follow the traditional publish-subscribe model. Which method is used to fire an event?

A developer must implement a CheckPaymentProcessor class that provides check processing payment capabilities that adhere to what defined for payments in the PaymentProcessor interface. public interface PaymentProcessor { void pay(Decimal amount); } Which is the correct implementation to use the PaymentProcessor interface class?

A developer declared a class as follow.
public class wysiwyg { // Properties and methods including DML }
Which invocation of a class method will obey the organization-wide defaults and sharing settings for the running user in the Salesforce Organization?

Universal Containers has a support process that allows users to request support from its engineering team using a custom object, Engineering Support c.
Users should be able to associate multiple Engineering Support __c records to a single Opportunity record. Additionally, aggregate information about the Engineering Support _c records should be shown on the Opportunity record.
Which relationship field should be implemented to support these requirements?

A developer wants to mark each Account in a List<Account> as either or Inactive based on the LastModified field value being more than 90 days.
Which Apex technique should the developer use?