Answer :
answer : 8 hours
hour 0 she has 15
hour 1 she has 16
hour 2 she has 17
hour 3 she has 18
hour 4 she has 19
hour 5 she has 20
hour 6 she has 21
hour 7 she has 22
hour 8 she has 23
hour 0 she has 15
hour 1 she has 16
hour 2 she has 17
hour 3 she has 18
hour 4 she has 19
hour 5 she has 20
hour 6 she has 21
hour 7 she has 22
hour 8 she has 23