Correct Answer - Option 3 : 4 hrs
Calculation:
Speed of upstream = 30/3 = 10 km/hr
Let the speed of current be x
∴ Speed of current = 12 – 10
= 2 km/hr
So, speed of downstream
= 12 + 2 = 14 km/hr
So, time taken to cover 56 km downstream = 56/14 = 4 hrs