Answer: Option C
$$\eqalign{
& {\text{Length of the train}} \cr
& {\text{ = Speed }} \times {\text{time}} \cr
& {\text{ = 36 km/hr}} \times {\text{10 sec}} \cr
& {\text{ = 36}} \times \frac{5}{{18}}{\text{m/s}} \times 10\sec \cr
& = 100{\text{ metres}} \cr
& {\text{Therefore, }} \cr
& {\text{Time taken by train to cross a plateform}} \cr
& {\text{ of 55 metre long in time}} \cr
& {\text{ = }}\frac{{\left( {100 + 55} \right)}}{{36 \times \frac{5}{{18}}}} \cr
& = \frac{{155}}{{10}} \cr
& {\text{Time}} = 15\frac{1}{2}\,\sec \cr} $$