The graph below shows the height of a tunnel f(x), in feet, depending on the distance from one side of the tunnel x, in feet: Graph of quadratic function f of x having x intercepts at ordered pairs 0, 0 and 36, 0. The vertex is at 18, 32.

Part A: What do the x-intercepts and maximum value of the graph represent? What are the intervals where the function is increasing and decreasing, and what do they represent about the distance and height? (6 points)

Part B: What is an approximate average rate of change of the graph from x = 5 to x = 15, and what does this rate represent? (4 points)