I have the following puzzles

I know that both air travel service(3 hours flight) and trains (36 hours on rails) are operating currently between HKSAR and Beijing.
Suppose that under the following circumstances :

• (a) the general real wage rate of the HKSAR citizens rises;
  

• (b) a fixed departure tax is imposed by the government no matter the HK people travelled by airplanes or trains;
  

How could you predict the impact on the change of number of travellers using airplanes (air passengers) and railways (rail passengers) from HKSAR to Beijing? (Hint: be resolved by the Law of Demand)