If the ratio of the height to the length is 1 to 6, we can write the following equation:
[tex]\frac{height}{length}=\frac{1}{6}[/tex]The height is equal to 30 ft, so let's solve the equation for the length:
[tex]\begin{gathered} \frac{30}{length}=\frac{1}{6}\\ \\ length=30\cdot6\\ \\ length=180\text{ ft} \end{gathered}[/tex]The length is equal to 180 ft, therefore the correct option is the fourth one.