100 obese people were asked about the number of hours they sleep each day. We want to test the hypothesis that obese people need more sleep than the general public who need an average of 7.7 hours of sleep. The sample mean is 6.0 and the population standard deviation is 0.3. In addition, the significance level is 0.05 with a theoritical Z = 1.645 . What is the Z score of the statistic test to be evaluated?
a. -56.66
b. -2.83
c. -1.645
d. 1.96