A truck travels at 90 km/hr for the first hours. After that it travels at 70 km/hr. Find the time taken by the truck to travel 310 kilometres.

[A]2.5 hours

[B]3 hours

[C]3.5 hours

[D]4 hours

**4 hours**

Distance covered by truck in hours = Speed Time

Remaining Distance = 310 – 135 = 175 km

∴ Time taken at 70 km/hr

∴ Total time = 1.5 + 2.5 = 4 hours

Hence option [D] is correct answer.