Answer:
1 3/7 hours
Explanation:
The planes are closing the 200 mile separation distance at a rate of (40 +100) = 140 miles per hour. The time it takes for that distance to be closed is ...
time = distance/speed
time = (200 mi)/(140 mi/h) = 200/140 h = 10/7 h = 1 3/7 h
The planes will meet after 1 3/7 hours, about 1 hour 25 minutes 43 seconds.