In order to test whether the average waiting time this year differs from last year, a sample of 25 data were collected this year with a mean of 0.74 hours and standard deviation 0.22 hours. Calculate the 99% confidence interval for the true waiting time for banking service this year.

a. 0.74 ± 2.57 x 0.22/√25
b. 0.74 ± 2.797 x 0.22/√25
c. 0.74 ± 2.797 x 0.22/√24
d. 0.74 ± 2.787 x 0.22/√25