During a 555-mile flight, a plane flew at two different speeds. For the first part of the trip, the average speed was 105 mph. Then the tailwind picked up, and the remainder of the trip was flown at an average speed of 115 mph. The entire trip took 5 hours. For how long did the plane fly at 115 mph?
Say the plane flew x miles at 115 mi/hr
since time = distance/speed,
x/115 + (555-x)/105 = 5