Refer to the data below and answer the questions that follow.
When BMW introduced its most advanced engine, it was found that the engine of the car followed certain mileage characteristics in a speed limit of 25 km/h to 80 km/h. The car can travel a distance of 15 km in one litre of petrol while speeding at 50 km/h. From this point onwards for every increase of 5 km/h in the speed of the car the mileage is increased by 1 km per litre. Similarly, for every decrease of 5 km/h in the the speed of the car, the mileage is decreased by 1 km per litre. Assume that the cars operate in this speed limit only.
In the previous question, what is the maximum span of time for which Rahul Ghosh can enjoy the drive?