Explanation:

- Boat Speed in Still Water: 15 m/s.

- Condition 1: Upstream speed is half the downstream speed.

- Find the downstream and upstream speeds:

- Let $x$ be the speed of the stream.

- Downstream speed = $15+x$.

- Upstream speed = $15-x$.

- Given that upstream speed $=\frac{1}{2}$ of downstream speed.

- So, $15-x=\frac{1}{2}(15+x)$.

- Solve to find $x=5$ m/s.

- Downstream speed of the boat: $20$ m/s.

- Speed of the Ship when it crosses the boat: Let it be $S$.

- $S-20$ m/s crosses the boat in 15 seconds.

- So, Length of the Ship = $15\times (S-20)$.

- Length of the boat = $50$ m.

- Length of the Ship = $100$ m.

- $100=15(S-20)$.

- Solve to find $S=26.67$ m/s.

- Ship’s Upstream Speed: $26.67-5=21.67$ m/s.

- Time to cover 144 kilometers (144,000 meters):

- Time = $\frac{144,000}{21.67}$ seconds = $6,646.72$ seconds.

- Convert to hours: $\approx 1.85$ hours.

None of the provided options is correct. However, the closest option is 1.6 hours.