Excluding stoppages, the speed of a bus is 54 kmph and including stoppages, it is 45 kmph. For how many minutes does the bus stop per hour ?

Answer: Option B

Due to stoppages, it covers 9 k less.
Time taken to cover 9 km :
$$\begin{array}{rl}& =\left(\frac{9}{54}\times 60\right)\text{ min}\\ & =10\min \end{array}$$