12 kilometers are equivalent to 4 trips.
To find how many trips are equivalent to 18 kilometers, we can use the next proportion:
[tex]\frac{12\text{ kilometers}}{18\text{ kilometers}}=\frac{4\text{ trips}}{x\text{ trips}}[/tex]Solving for x:
[tex]\begin{gathered} 12\cdot x=4\cdot18 \\ x=\frac{72}{12} \\ x=6 \end{gathered}[/tex]Mackenzie have to make 6 trips to walk 18 kilometers.
