I have not heard of

*specification hours*. It looks like you are supposed to calculate the confidence interval with 95% confidence level.

The Central Limit Theorem (which the general rule of thumb says is ok to invoke for

) tells us that

is approximately normally distributed with mean 0 and std dev 1.

So then the confidence interval is given by

where

is defined by

(

*Z* is from the standard normal distribution). I'm assuming that you have already seen where these formulas came from.

So from a standard normal distribution table

. So just plug away.