6.) A car company claims that they increased the MPGs for its cars. Below are MPGs in 2015 and then in 2020 of some of their models: 2015 23 33 25 30 27 24 2020 25 36 25 32 29 25 At a=0.05, can we claim that the mean difference is less than zero? Does the manufacturer have a valid claim? Test using: a.) a hypothesis test b.) a confidence interval