Find the sample size necessary to estimate the mean weight of all supermodels so that there is

Question:

Find the sample size necessary to estimate the mean weight of all supermodels so that there is 95% confidence that the sample mean is in error by no more than 2 lb. Assume that a pilot study suggests that the weights of all supermodels have a standard deviation of 7.5 lb.

Use the following weights (in pounds) of randomly selected supermodels.