A journal published a study of the lifestyles of visually impaired students. Using​ diaries, the students kept track of several​ variables, including number of hours of sleep obtained in a typical...

A journal published a study of the lifestyles of visually impaired students. Using​ diaries, the students kept track of several​ variables, including number of hours of sleep obtained in a typical day. These visually impaired students had a mean of

hours and a standard deviation of

hours. Assume that the distribution of the number of hours of sleep for this group of students is approximately normal. Complete parts a through c.

a. Find

​(Round to four decimal places as​ needed.)

b. Find

​(Round to four decimal places as​ needed.)

c. Find the value a for which