To solve the exercise you can use a rule of three, like this
[tex]\begin{gathered} \frac{3}{4}\text{mi}\rightarrow\frac{3}{10}\text{hour} \\ x\text{ mi}\rightarrow1\text{ hour} \end{gathered}[/tex][tex]\begin{gathered} x=\frac{1\text{ hour}\cdot\frac{3}{4}\text{ mi}}{\frac{3}{10}\text{ hour}} \\ x=\frac{1\cdot\frac{3}{4}\text{ mi}}{\frac{3}{10}} \\ x=\frac{1\cdot\frac{3}{4}}{\frac{3}{10}}\text{ mi} \\ x=\frac{\frac{3}{4}}{\frac{3}{10}}\text{ mi} \end{gathered}[/tex]To divide fractions you operate like this
[tex]\frac{\frac{a}{b}}{\frac{c}{d}}=\frac{a\cdot d}{b\cdot c}[/tex]Then, you have
[tex]\begin{gathered} x=\frac{\frac{3}{4}}{\frac{3}{10}}\text{ mi} \\ x=\frac{3\cdot10}{4\cdot3}\text{ mi} \\ x=\frac{10}{4}\text{ mi} \\ x=\frac{5}{2}\text{ mi} \\ x=2.5\text{ mi} \end{gathered}[/tex]Therefore, Zalmon's speed is 2.5 miles per hour.