(a) Solve for the upper and lower limit of the average.
[tex]\begin{gathered} \text{Upper Limit} \\ 9.72+0.22=9.94 \\ \\ \text{Lower Limit} \\ 9.72-0.22=9.5 \end{gathered}[/tex]
Therefore, the average length of a motor vehicle trip in the United States is between 9.5 and 9.94 miles.
(b) The level of conficence for this estimate as stated in the given problem is 95%.
