Let the speed of the train be \( v \, \text{m/s} \). The time taken to cross a pole is 18 seconds, which implies the length of the train is \( 18v \). The time taken to cross a platform is 36 seconds, implying the total distance covered (train length + platform length) is \( 36v \). Therefore, \( \text{Total distance} = \text{Length of train} + \text{Length of platform} = 18v + 200 \).
\[36v = 18v + 200 \Rightarrow 18v = 200 \Rightarrow v = \frac{200}{18} \approx 11.11 \text{ m/s}\]Note: The nearest option is 10 m/s.