a computer store sells two types of computers, desktops and laptops. The supplier demands that at least 150 computers be sold a month. In order to keep profits up, the number of desktops sold must be at least twice of laptops. The store pays its sales staff a $75 commission for each desktop, and a $50 commission for each laptop. How many of each type of computers must be sold to minimize commission to its sales people? what is the minimum commission?