Has the average cost of water increased? In the past, the population mean water cost was $135 per quarter with a population standard deviation of $10. A recent sample of 30 households had a mean of $140 per quarter. Assume the conditions are satisfied, and do NOT need to be checked here.

a) Write the hypotheses to answer the question.

b) SHOW BRIEF CALCULATIONS, for the calculated test statistic.

c) Give the critical value, if using the 10% level of significance.

d) Give your decision.

e) Give your conclusion, in the context of answering the initial question.