Question 245
After one hour, the first plane moves westward by 540 miles, and the second will move eastward by 720 miles. The distance between them (ignoring curvature of the Earth) will be 540+720 miles, that is, 1260 miles. So, the distance is incrreasing by 1260 miles per hour. To find out how long it will take them to become 1890 miles apart, you need to divide 1890 by 1260. The answer to that is left as an exercise to you.