an automobile manufacturer has given its van a 31.0 miles/gallon (mpg) rating. an independent testing firm has been contracted to test the actual mpg for this van since it is believed that the van performs over the manufacturer's mpg rating. after testing 150 vans, they found a mean mpg of 31.2. assume the population standard deviation is known to be 2.1. is there sufficient evidence at the 0.02 level to support the testing firm's claim? step 1 of 6 : state the null and alternative hypotheses.