Marvin runs a bookstore. He has determined that the profit he receives from selling self-help books is a quadratic function of the price per book he chooses to charge his customers. If he sells the books for $0, he is giving them away and will obviously earn $0 in profit. If he sells them for $30 each, they are too pricey and he won't sell any and also end up with $0 profit. Currently he sells the books for $25 each and his weekly profit is $62.50