Asample of 9 production managers with over 15 years of experience has an average salary of $71,000 and a sample standard deviation of $18,000. assuming that s = 18,000 is a reasonable estimate for f$sigma f$ 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, in the blank. do not use a dollar sign, a comma, or any other stray mark. for examples, 34 would be a legitimate entry.