Correct Answer: 8 hrs
Explanation:
Speed upstream = (6 - 1.5) km/hr = 4.5 km/hr Speed downstream = (6 + 1.5) km/hr = 7.5 km/hr Total time taken = (22.5/4.5 + 22.5/7.5) hrs = (5 + 3) hrs. = 8 hrs.