Warby's Inc serves 900 customers during a 15 hour day. A customer spends 2 minutes waiting in line inside the premises, 3 minutes placing the order, and 5 minutes collecting the order before leaving the premises. About how many customers on average are inside the premises (i.e., from the time they enter to the time they exit) on a typical day (Use Little's law) a) 5 b) 10 c) 30 d) 40