Final answer:
The values of x for which f(x) = 0 are between 0 and 20, inclusive.
Step-by-step explanation:
To find the values of x for which f(x) = 0, we need to determine where the horizontal line representing f(x) intersects the x-axis. In this case, since the graph of f(x) is a horizontal line, it intersects the x-axis at every value of x between 0 and 20, inclusive. Therefore, the values of x for which f(x) = 0 can be written in interval notation as [0, 20].