28/ A research study examined the effects of meditation on quality

of sleep. Fifty individuals were asked how many nights, on average, they lost sleep at the beginning of the study. Then all fifty individuals were placed into a meditation intervention every day for three months. At the end of the three months, the same fifty individuals were asked how many sleepless nights they had on average. The mean difference between the before and after intervention groups was 5.6 nights, with a standard deviation of 5. Calculate the z, t, or chi-square test and choose the value in the answer below.
Select one:
a. 6.15
b. 7.92
c. 8.23
d. 7.21