$6.$ After a long flight, you arrive in Buenos Aires and go through immigration. An immigration officer at the Ezeiza International Airport handles two different types of travelers: citizens from countries requiring a visa to enter Argentina and citizens from those countries that do not require a visa. Because of the different documentation and verification requirements, the officer can process the first type of traveler at a rate of $15$ per hour, and that type represents $20\%$ of the arriving travelers. The officer can process citizens of other countries at a rate of $40$ per hour, and that type represents $80\%$ of all arriving travelers. What is the average processing rate $($expressed in travelers per hour$)$ at which this officer can handle total arriving travelers, assuming they come in according to the specified mix?