According to the local president the mean income of plumbers is normally distributed with a mean of $60,000 and a population standard deviation of $ 6000. An Investigative reporter for the local television took a sample to try to disprove that claim. The sample size consisted of 20 plumbers with a mean Income of $62,500 . At the 5% level of significance , is it reasonable to conclude that the mean income different than $60,000?

a. determine the critical value

b. Calculate the test statistic

c.calculate the pvalue

d.what is your decision about the null hypothesis?