A motorboat can travel in still water at the speed 15 km/h, while the speed of the current is 3 km/h. Time taken by boat to go 36 km upstream is :

3 hr

The correct answer is Option (2) → 3 hr

Speed upstream = Speed in still water - Speed of current

$=15-3$

$=12km/hr$

$\text{Time} = \frac{\text{Distance}}{\text{Speed}}=\frac{36}{12}=3\,\text{hours}$