The graph shows the number of visitors V to a national park in hundreds of thousands during a one-year period, where t = 1 represents January.

(a) Estimate the rate of change of V over the interval [9, 12] and explain your results.

---

(b) Over what interval is the average rate of change approximately equal to the rate of change at Explain your reasoning.

Number of visitors of thousands) (in hundreds Visitors to a National Park V 1500 1200 900 600 300 1 2 3 4 5 6 7 8 9 10 11 12 Month (1 January)