Explanation:

Let’s break it down step by step:

- We’ve got two scenarios:

- 30 km downstream + 24 km upstream = 2 hrs 27 mins (Or 147 mins, which is 2.45 hours)

- 10 km downstream + 4 km upstream = 37 mins (Or about 0.6167 hours)

- Let’s say downstream speed = D, upstream speed = U.

- So, equations:

- (30/D) + (24/U) = 2.45

- (10/D) + (4/U) = 0.6167

- The trick is: solve these equations.

- Multiply the second equation by 3:

- (30/D) + (12/U) = 1.8501

- Subtract this from the first equation:

- [(30/D) + (24/U)] - [(30/D) + (12/U)] = 2.45 - 1.8501

- (24/U) - (12/U) = 0.5999

- (12/U) = 0.5999

- U = 12 / 0.5999 ˜ 20 km/hr

- So, upstream speed is 20 km/hr.

Now, let’s look at the options:

- Option 1: 18 – nope, too low.

- Option 2: 20 – this is the one.

- Option 3: 22 – not matching.

- Option 4: 24 – too high.