Answer:v=142.85 mph
Step-by-step explanation:
Given
Distance between two cities is 1000 miles
Speed of plane 1 id 250 mph
Plane 1 leaves at 7 am and Plane 2 leaves at 7:30 am
They will collide if plane 2 travels 300 miles and Plane 1 travels 400 miles in t and t+0.5 hr respectively
Time taken by plane 2
----1
time taken by plane 1 to travel 400 miles
-----2
substitute value of t in 2