All contact's mailing post code should match the account shipping postal code.How to do it?

After universal containers converted qualified leads. Sales reps need to be able to report on converted leads. How should an app builder support for this requirement ?

Universal Containers has Public Read/Write as the Account organization-wide default (OWD) setting. Visitors to the customer community site report that they can see all of the company's account records.
How should an app builder configure Account sharing so that community users only see their own Account?

Sales reps at Universal Containers use Salesforce on their mobile devices. They want a way to odd new contacts quickly and then follow up later to complete the additional Information necessary.
What mobile solution should an App Builder recommend?

A manager wants to calculate the number of days an account has been last contacted through mail. Which field should be used to achieve this?