A store sells packages of comic books with a poster. A poster and 8 comics cost $15.75. A poster and 13 comics cost $20.75.Write a linear function rule that models the cost y of a package containing any number x of comic books. Suppose another store sells a similar package, modeled by a linear function rule with initial value $8.99. Use pencil and paper. Explain which store has the better deal. The linear function rule is y__.