A Simple Random Sample of Kitchen Toasters Is to Be $\sigma = 20$

Multiple Choice

A simple random sample of kitchen toasters is to be taken to determine the mean operational lifetime in hours. Assume that the lifetimes are normally distributed with population standard deviation $\sigma = 20$ hours.
Find the sample size needed so that a $98 \%$ confidence interval for the mean lifetime will have a margin of error of 8 .

A) 117
B) 5
C) 6
D) 34