How many seals were present in 2011: 30. How long does it take the family to reach the beach: 2 hours. How long does the family spend at the beach: 4 hours. What is the average rate of change between 0 and 2 hours: 45 kmh. What is the average rate of change between 6 and 10 hours: 22.5 kmh. At what time is the rocket the highest according to the graph: 120 seconds. Where is the average rate of change the largest: Between 20 and 40 seconds. What is the average rate of change from 0 to 40 seconds: 0.15 mps.. Which person is running the fastest: A. At what distance does the motorcycle pass the car: 50 m.