I need to see the calculation in order to grasp the idea.

Planners for the WarmUp Co. want to estimate how much damaged inventory they will have throughout the year.In particular, they are concerned with the "number of broken coffee mugs per shipping crate of mugs."Looking at recent shipments they found that, on average, 4.7 mugs were broken per crate.This estimate was obtained from a sample of 60 crates.The sample standard deviation was s = 2.1 mugs.WarmUp projects future shipments to have the same breakage rate as this sample.What is the 95% confidence interval for the average number of broken mugs per shipping container?