Robert is ordering a taxi from an online taxi service. He has to pay a flat charge just to order the taxi, and then has to pay per mile, depending on how far he travels. He wrote an equation to represent his total cost, y, equals, 4, point, 5, plus, 1, point, 5, xy=4.5+1.5x, where yy represents the total cost in dollars and cents, and xx represents the number of miles he travels. What could the number 4.5 represent in the equation?