A car can finish a certain journey in 10 hours at a speed of 42 kmph. In order to cover the same distance in in 7 hours, the speed of the car (km/h) must be increased by :

Answer: Option C

Total distance :
= 42 × 10
= 420 km
New given time = 7 hr and
Required new speed :
= $$\frac{420}{7}$$ km/hr
= 60 km/hr
∴ Required increase in speed :
= (60 - 42) km/hr
= 18 km/hr