The question is about calculating the speed for a quarter of the journey. The car travels 3/4th of the distance at 60 km/hr and the remaining 1/4th of the distance at an unknown speed v km/hr. Given that the average speed of the entire journey is 50 km/hr, we need to find the value of v.

Option 1 suggests the unknown speed is 40 km/hr. But if it was the case, the average speed would have been more than 50 km/hr when combined with the speed of the majority of the journey.

Option 2 suggests 30 km/hr which would lead to even lesser average speed than provided.

Option 3 is the correct answer with v = 100/3 km/hr (approximately 33.33 km/hr). If you calculate with these speeds for respective distances, you can reach an average speed of 50 km/hr for the distance travelled giving credence to this option.

Option 4 having v = 35 km/hr, similar to option 1, would create higher average speed than the given one making it incorrect.