Mitchell plays a trading card game. He has the starter pack of cards and adds to his collection by purchasing a booster pack each week that contains the same number of cards. On the graph, points are plotted and a line is drawn through the points to show the linear relationship between the total number of cards in Mitchell's collection and the number of weeks he has been collecting. Mitchell's Trading Card Collection 225 210 195 Total Number of Cards 180 165 150 135 120 105 90 75 60 45 30 15 0 0 2 8 5 6 7 Number of Weeks a What is the initial value of the function represented by the graph? b. What is the rate of change of the function represented by the graph? = 60​