Please help for test

A butcher shop manager wants to know how much on average customers spend per visit. Previous research suggests that the population standard deviation is $16.78. The manager found a mean value of $72.50 for a random sample of 60 customers, and wants to construct a 95% confidence interval for the mean value. Round your answers to 3 decimal places where appropriate. (a) What is the critical z-value that will need to be used to calculate the confidence interval? (b) What is the 95% confidence interval? :] (c) If the manager wants a margin of error within $1, how large of a sample size will they need? :]