To solve this problem we will apply the concepts related to relative speed. We will obtain it from the deduction made on the aircraft as a speed of the two components that act on it. Through the kinematic equations of motion, we can then calculate the time required.
The airspeed of airplane is 100km/h while the wind is blowing from the coast out to sea at 40km/h. Wind is blowing from the coast out to sea means that it opposes the airspeed. Therefore, resultant relative speed of airplane is
Total distance is 60km then with this net velocity we have that the required time is
Where,
x = Displacement
t = Time
v = Velocity
Replacing,
Therefore the time taken by the plane to reach the shore is 60 minutes