Is smoking during pregnancy associated with premature births? To investigate this question, researchers selected a random sample of 104 pregnant women who were smokers. The average pregnancy length for this sample of smokers was 263 days. From a large body of research, it is known that length of human pregnancy has a standard deviation of 16 days. The researchers assume that smoking does not affect the variability in pregnancy length.

Find the 99% confidence interval to estimate the length of pregnancy for women who smoke.

(Note: The critical z-value to use, zc, is: 2.576)