The results of a national survey showed that on average, adilts sleep 6.8 hours per night, 5 uppose that the standard deviation an 1.4 hours and that the nunter if heirs of sleep follows a bell-shaped distribution. If needed, found your answers to two decimal digits. If your answer is negaine use "makis sigh" (a) Use the empirical nule to calculate the percentage of individuals who sleep between 4 and 9.6 hours per dlay. Enter your answer as a percentage. (b) What is the z-value for an adialt who sleeps 8 hours per night? (c) What is the z-value for an adult who sleeps 6 hours per night?