Answer:
Plane one = 4.5 hours
Plane two = 2.25 hours
Explanation:
We know that speed of plant one to be 300 miles per hour and plane two 600 miles per hour we can determiine the time they will take to be 2700 part. Speed is defined as:

Were v is the velocity, d the distance, t the time
For the the two planes to be 2700 miles apart from the same point they will have travelled half of 2700 miles from that point. Therefore they travel 1350 miles each.
For plane one we can calculate the time from the speed equation:


For plane two:


Plane one will take 4.5 hours and plant two 2.25 hours to be 2700 miles apart