Answer:
The rate of the jet in still air is 1125 miles per hour, and the rate of the wind is 375 miles per hour.
Explanation:
Flying against the wind, the speed of the airplane is 750 miles per hour (3000/4), while flying with a downwind, its speed is 1500 miles per hour (7500/6). Therefore, the difference between the two speeds is 750 miles per hour, so since the distance traveled is the same, the midpoint between the two speeds is 375 miles per hour. Then, without wind, the plane would travel the same distances at a speed of 1125 miles per hour.
In conclusion, the rate of the jet in still air is 1125 miles per hour, and the rate of the wind is 375 miles per hour.