The personnel department of a large corporation wants to estimate the family dental expenses of its employees to determine the feasibility of providing a dental insurance plan. A random sample of 10 employees reveals the following family dental expenses (in dollars) for the preceding year:

110 362 246 85 510 208 173 425 316 179

You are asked what is 95% Confidence Interval for the average family dental expenses for all employees of this corporation.

a) What is the sample average? Calculated: 261.4

b) What is the sample standard deviation? Calculated: 138.80

c) What is a 95% CI for the true average family dental expenses for this company? I need calculation of this section, and clear breakdown on how from 95% Z is calculated.