The lookout on board a ship spots an unknown ship on the open seas and immediately
alerts Chris, the ship's captain. The unknown ship is currently 4 miles south and 3 miles
east of Captain Chris's ship, and it is at that moment sailing due west at 20 mph. Captain Chris's ship, meanwhile, is at that moment sailing due north at 16 mph. Is the distance between Captain Chris's ship and the unknown ship increasing or decreasing? How fast? (Distance is measured along a straight line joining the two
ships.)

Question