I found the equation which was the pythagoras theorem and then took the derivative of the equation but not sure what to plug in where. Oh and I found C(t) to be 743.30

Question

An airplane passes over an airport at noon traveling 500 mi/hr due
West. At 1:00 pm, another airplane passes over the same airport at the same
elevation traveling due North at 550 mi/hr. Assuming both planes maintain their
(equal) elevations, how fast is the distance between them changing at 2:30 pm?