Let speed of train and bus be x and y respectively.

Then as given in the first condition, it takes four hours for a 300 km journey, if 200 km is done by train and the rest by bus

⇒ total time taken $(= \frac{{200}}{x} + \frac{{100}}{y} = 4)$

$(\Rightarrow \frac{2}{x} + \frac{1}{y} = \frac{1}{{25}})$        ----(i)

As given in the second case, it takes 30 minutes more, if 150 km is done by train and the rest by bus.

⇒ total time taken $(= \frac{{150}}{x} + \frac{{150}}{y} = 4 + \frac{{30}}{{60}} = \frac{9}{2})$

$(\Rightarrow \frac{1}{x} + \frac{1}{y} = \frac{3}{{100}})$        ----(ii)

Solving (i) and (ii), we get:

x = 100, y = 50