The engine of a bus follows certain mileage characteristics in a speed limit of 25 km/hr to 80 km/hr. The bus can travel a distance of 15 km in one litre of petrol while travelling at 50 km/hr. From this point onwards for every increase of 5 km/hr in the speed of the bus the mileage is increased by 1 km per litre. Similarly for every decrease of 5 kmph in the speed of the car the mileage is decreased by 1 km per litre. Assume that the bus travels in this speed limit only. Krishna has filled exactly 10 litres of petrol in his bus. He drives at a speed of 45 kmph for first two hours. What is maximum distance that he can cover with the remaining quantity of petrol before his tank empties?