Price of the plane ticket = $600
Price of the bus ticket = $150
Additional money for plane ticket = 600-150 =$450
Time taken by air travel = 6 hours
Time taken by bus travel = 51 hours
Time saved by air travel = bus travel time - air travel time = 51-6 = 45 hours
So, for savings 45 hours, you spend $450 more for the plane travel
So the individual would only gain if his value is time is greater than Amount spend on plane/saved time
So the individual would only gain if his value is time is greater than $450/45 hr=$10/hr
Other things constant, an individual would gain by choosing air travel if, and only if, his time were valued at more than $ 10 per hour