Answer: the speed of the plane is 45 miles per hour
Explanation:
The plane travelled 240 miles to Miami and back from Miami. This means that he travelled 120 miles while going and 120 miles while coming back. The trip while going with the wind took 2 hours.
Speed = distance / time
The speed while going with the wind = 120/2 = 60 miles per hour
The trip while going against the wind took 4 hours.
The speed while going against the wind = 120/4 = 30 miles per hour
Let x = the speed of the plane
Let y = the speed of the wind
While going,
x + y = 60 - - - - - - - 1
While coming back against the wind,
x - y = 30 - - - - - 2
Subtracting equation 2 from equation 1,
2y = 30
y = 30/2 = 15 miles per hour
x = 60-y = 60-15
x = 45 miles per hour