Correct Answer - Option 3 : 18 km/h
Let V be the average speed of the car in the second half of travel.
As we know, overall average speed of the car = (Total distance covered)/(Total time taken)
⇒ 27 = (72 + 63)/(72/48 + 63/V)
⇒27 = 135/(1.5 + 63/V)
⇒ 1.5 + 63/V = 135/27 = 5
⇒ 63/V = 5 – 1.5 = 7/2
⇒ V = 9 × 2 = 18 km/h