Answer:
[tex]unit \: rate = \frac{distance}{time} \\ [/tex]
substitute:
[tex]unit \: rate = \frac{( \frac{1}{2} )}{ ( \frac{3}{4}) } \\ \\ = \frac{1}{2} \div \frac{3}{4} \\ \\ = \frac{1}{2} \times \frac{4}{3} \\ \\ = \frac{4}{6} \\ \\ = { \underline{ \: \: \frac{2}{3} \: \: miles \: per \: hour \: \: }}[/tex]