I have like 9 more of these problems, can someone please help me out so I can get started. thanx JS

In a random sample of 35 tractors, the annual cost of maintenance was $4,425 and the standard deviation was $775.

Construct a 90% confidence interval for this.

Assume the annual maintenance costs are normally distributed.

A visit to

http://davidmlane.com/hyperstat/z_table.html

may help. It shows how the Z table works, without your having to look up the numbers. If you have a Z table handy as you use the tool, it should clear things up.