we're examining the car accident rate in pennsylvania by county. let's say that the average number of accidents is 56 per day. let's further say that the county with the lowest accident rate had 9 accidents a day, while the county with the highest rate had 105 accidents a day. in other words, 100% of the data fall between 9 a day and 105 a day. using the empirical rule (68-95-99.7), what is the best guess for this distribution's sd?