The speed of a boat in still water is 12 km/h and the speed of the stream is 2 km/h. A person rows to a place at a distance of 70 km and returns back to the starting point. What is the total time taken by him ?

12 hours

The correct answer is option (1) : 12 hours

$∵ d=\frac{t(x^2-y^2)}{2x}$

$70= \frac{t(12^2-2^2)}{2×12}$

$t = 12 \, hours $