Ms. Liu tells you that on each weekday, visitors return to her website an average of twice, and on weekends, visitors return four times per day. She adds that these two groups of users are different. She wants to know how many unique visitors (i.e., the number of users who visit the site, regardless of the number of their visits) visit her site on weekdays and weekends. Please note that if a particular visitor comes to the site every day or several times a day, it still counts as only one visit.