a clerk in a bookstore has 90 minitues at the end of each workday to process orders recieved by mail or on voice mail. The store has found that a typical mail order brings in a profit of $30 and a typical voice - mail order brings in a profit of $40. Each mail order taakes 10 minutes to process and each voice-mail order takes 15 minutes. How many of each type of order should the clerk process in order to maximize their profit.