Robert has entered a competition in which he must drive from his home town of Paris to London, a distance of approximately 450 km. If he arrives in: • 6 hours (an average speed of 75 km/h), he will receive a prize of €400 • 8 hours (an average speed of 56.25 kmh), he receives €370 As per the competition rules, he must pay for his own gasoline, Robert has calculated that he will average: • 25 km per liter at 75 km/h • 30 km per liter at 56.25 km/h Assume that the price of gasoline is 4 per liter. To maximize his winnings (prize money minus the cost of gasoline), Robert must drive at a speed of km/h, (Enter your response as an integer)