How are Publication Lists used?

Northern Trail Outfitters received an email about reaching API limits within Salesforce and they think this is caused by the integrated Marketing Cloud account.
Which two types of API calls are counted against the rolling 24-hour limit?

A company collects subscriptions on its website. It does the following:
* Compiles that subscription list in a database in the website Content Management System (CMS).
* Posts this encrypted list to Marketing Cloud nightly at 11 p.m.
* Uses Marketing Cloud as the database of record.
* Sends up to five emails a week based on subscriber engagement with prior sends.
Which automation sequence (excluding waits) should cover these requirements?

A customer notices their open and click rates are very low.
Which two aspects of list hygiene should be recommended to improve engagement rates? (Choose 2 answers)

A customer frequently holds seminars and other events to interface with their customers. They plan to do the following:
*Use SmartCapture forms to write data into event registration data extensions.
*Cross-reference the records in each registration data extension with corresponding invitation email sends.
*Send a follow-up email to customers who click on the registration link in the invitation email, but do not complete registration.
Which skill is needed to build an efficient solution?