An airplane cruises at 850 km/h relative to the air. It is flying from Denver, Colorado, due west to Reno, Nevada, a distance of 1200 km, and will then return. There is a steady 90km/h wind blowing to the east.

difference in flight time = 0.3023 hour

Explanation:

The question is incomplete, but I found it in your textbook.

Spped of aircraft = 850 km/h

Opposing speed of wind = 90km/h

Hence, the net speed when it's travelling west = 850 - 90 = 760 km/hr

The distance covered = 1200km

time taken = distance / time = 1200 / 760 = 1.5789 hours

When coming back, the speed of the wind is complementary to the speed of the aircraft so

net speed when it's coming back = 850 + 90 = 940 km/hr

time taken in this instance = 1200 / 940 = 1.2765 hours

Hence, the difference in flight time = 1.5789 - 1.2765 = 0.3023 hour