An engineer has designed a valve that will regulate water pressure on an automobile engine. the valve was tested on 200 engines and the mean pressure was 5.4 pounds/square inch (psi). assume the population standard deviation is 0.8. the engineer designed the valve such that it would produce a mean pressure of 5.5 psi. it is believed that the valve does not perform to the specifications. a level of significance of 0.05 will be used. find the value of the test statistic. round your answer to two decimal places.