Let X denote the crop yield of corn measured in the number of bushels per acre. Assume (unrealistically) that X is normally distributed with unknown mean and standard deviation = 6. An agricultural researcher is working to increase the current average yield from 40 bushels per acre. Therefore, he is interested in testing, at the a = 0.05 level, the null hypothesis h0: u = 40 against the alternative hypothesis that ha: u > 40. Find the sample size n that is necessary to achieve 0.90 power at the alternative.