The y-intercept of the graph of y = 19.99 + 1.50x in the xy-plane is the point on the graph with an x-coordinate equal to 0. In the model represented by the equation, the x-coordinate represents the number of miles a rental truck is driven during a one-day rental, and so the y-intercept represents the charge, in dollars, for the rental when the truck is driven 0 miles; that is, the y-intercept represents the cost, in dollars, of the flat fee. Since the y-intercept of the graph of y = 19.99 + 1.50x is (0, 19.99), the y-intercept represents a flat fee of $19.99 in terms of the model.