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 120, 0. The vertex is at 60, 35.

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?

Part B: What is an approximate average rate of change of the graph from x = 20 to x = 35, and what does this rate represent?