Suppose an automobile manufacturer designed a radically new lightweight engine and wants to recommend the grade of gasoline that will have the best fuel economy. the four grades are regular, economy, premium, and super premium. the test car made three runs on the test track using each of the four different grades of gasoline (i. e there were a total of 12 test runs). the miles per gallon were recorded for each grade. at the 0.05 level, what is the critical value of f used to test the hypothesis that the miles per gallon for each fuel are the same