Speed = \(\frac{Distance}{Time}\)

⇒ Time = \(\frac{Distance}{Time}\)

Let D = distance between the two airports

∴ Time taken to get to the airport = \(\frac{D}{120}\) and Time taken to return =\( \frac{D}{150}\)

Since total time of flight= 3hours,

⇒ \(\frac{D}{120} + \frac{D}{150}\) = 3

⇒ \(\frac{15D + 12D}{1800}\) = 3

⇒ \(\frac{27D}{1800}\) = 3

⇒ \(\frac{3D}{200} = \frac{3}{1}\)

⇒ 3D = 200 x 3

∴ D =\(\frac{ 200\times3}{3}\)= 200km