plz help me on my statistcs hw

Question

The age when smokers first start from previous studies is normally distributed with a mean of 13 years old with a population standard deviation of 1.3 years old. A survey of smokers of this generation was done to estimate if the mean age has changed. The sample of 34 smokers found that their mean starting age was 14.6 years old. Find the 99% confidence interval of the mean.

Answer 1

CI = mean +/- critical value for 99% CI * standard deviation/square root(sample size)

critical value for 99% CI is found by looking up z-score for probability 0.995 ~= 2.58

mean is given as 14.6, standard deviation is given as 1.3 and sample size is given as 34.

plug numbers into formula get CI.