Step 1 :The null hypothesis (H0) is the statement that the mean braking distances for the two makes of automobiles are equal, while the alternative hypothesis (Ha) is the statement that the mean braking distances for the two makes of automobiles are not equal.
Step 2 :So, the null hypothesis (H0) and the alternative hypothesis (Ha) are: \[\begin{array}{l} H_{0}: \mu_{1}=\mu_{2} \\ H_{a}: \mu_{1} \neq \mu_{2} \end{array}\]
Step 3 :Therefore, the final answer is \[\boxed{\begin{array}{l} H_{0}: \mu_{1}=\mu_{2} \\ H_{a}: \mu_{1} \neq \mu_{2} \end{array}}\]