Open Question: Confidence interval for the population mean?

Confidence interval for the population mean: Use of the standard normal

The union for a particular industry has determined that the standard deviation of the daily wages of its workers is $15. A random sample of 50 workers in this industry has a mean daily wage of $117. Find a 90% confidence interval for the true mean daily wage of all union workers in the industry.

I need to know what the upper 90% is, and what the lower 90% is. Thanks for helping me out I really appreciate it!

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