Let x be the train' speed, in km/h Then the plane speed is 2x km per hour. The train spendshours to cover the distance of 240 km. The plane spends hours for the same trip. The condition says that the difference in time is 1 hour: - = 1. Multiply bot sides by 2x. You will get 2*240 - 240 = 2x ====> 2x = 240 ====> x = = 120. Thus you found the speed of the train. It is 120 km/h. Then the speed of the plane is 2*120 = 240 km/h.