A z-test is to be performed for a population mean. Express the decision criterion for the hypothesis test in terms of x. That is, determine for what values of x the null hypothesis would be rejected. After training intensively for six months, John hopes that his mean time to run 100 meters has decreased from last year's mean time of 11.8 seconds. He performs a hypothesis test to determine whether his mean time has decreased. Preliminary data analyses indicate that it is reasonable to apply a z-test. The hypotheses are Ho: 11.8 seconds H: