How much do students pay, on the average, for textbooks during the first semester of college? From

Question:

How much do students pay, on the average, for textbooks during the first semester of college? From a random sample of 400 students the mean cost was found to be $357.75, and the sample standard deviation was $37.89. Assuming that the population is normally distributed, find the margin of error of a 95% confidence interval for the population mean.