For Exercises 16, assume that you want to construct a 95% confidence interval estimate of a population

Question:

For Exercises 16, assume that you want to construct a 95% confidence interval estimate of a population mean. Find an estimate of the sample size needed to obtain the specified margin of error for the 95% confidence interval. The sample standard deviation is given.
Margin of error = 0.5 g, standard deviation = 8.7 g