Mark and Andrew both drove to a new arena and both went to the valet parking section. Mark drove a Ford Focus and Andrew drove a Porsche 911. What would be the total tip the valet attendant should get from the both of them?

Some professions that provide you with personalized service don't pay well and so they expect a tip - waiters and waitresses, cab drivers, tour guides, hotel bell hops (yes they do still exist in many places), hotel maids, valet attendants (they park your car for you), movers and barbers and hair dressers.  
Often, tips are based on percentages.