An appliance manufacturer claims to have developed a compact microwave oven that consumes a mean of no more than 250 W. From previous studies, it is believed that power consumption for microwave ovens is normally distributed with a population standard deviation of 15 W. A consumer group has decided to try to discover if the claim appears true using a 5% level of significance. They take a sample of 20 microwave ovens and find that they consume a mean of 257.3 W. What is the critical value with a level of significance of 0.05 and what is the test statistic and what is the p value?