A company manufactures wind turbines. A random sample of 25 turbines is taken and the sample mean life is 20.00 years with a standard deviation of 2.50 years. If you were constructing a 90% two-sided confidence interval estimate, the upper limit would be ..
Go through a similar process as mentioned in your later post.
However, now Z = (x - μ)/SD, but you need to consult that table for the proportion to find the Z score.