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A sample of 9 production managers with over 15 years of experience has an average salary of $71,000 and a sample standard deviation of $18,000.

Assuming that s = 18,000 is a reasonable estimate for

what sample size would be needed to ensure that we could estimate the true mean salary of all production managers with more than 15 years experience within $4200 if we wish to be 95% confident? Place your answer, as a whole number, do not include a decimal, in the blank. Donotuse a dollar sign, a comma, or any other stray mark. For examples, 34 would be a legitimate entry.___