The snow fell at first, then stopped snowing for a number of hours. During the time the snow stopped falling, the inches of snow on the ground stayed the same. A constant function is represented by a horizontal line.
On our graph, we have a horizontal line between 6 hours and 12 hours after the snowstorm start.
The value of the function on this interval represents the amount of snow when it stopped snowing the first time. The corresponding function value is 4 inches.