The equation y = 19.99 + 1.50x models the total cost y, in dollars, that a company charges a customer to rent a truck for one day and drive the truck x miles. the total cost consists of a flat fee plus a charge per mile driven. when the equation is graphed in the xy-plane, what does the y-intercept of the graph represent in terms of the model? a) a flat fee of $19.99 b) a charge per mile of $1.50 c) a charge per mile of $19.99 d) total daily charges of $21.49