I'm trying to figure out which formula to use. A sample of 1,000 U. households is taken and the average amount of newspaper garbage or recycling is...

I'm trying to figure out which formula to use.

A sample of 1,000 U.S. households is taken and the average amount of newspaper garbage or recycling is found to be 27.8 pounds. Assume the standard deviation of newspaper for garbage or recycling is 2 pounds. Estimate, with 90% confidence, the mean amount of newspaper garbage or recycling for the American households.

Keep intermediate steps to four decimals when possible & enter your answer to two decimals.