**Answer**: (D) 6.30 a.m.

**Explanation**: Total Distance = 24 km (Suppose), At 11 a.m. he covers 9 km, at 4:30 p.m. he covers 20 km

Hence, he covers (20 – 9) = 11 km in 5(1/2) hours.

His speed = 2 km/h. To cover the first 9 km he takes 4(1/2) hours.

He started his journey at 6:30 a.m.