First, you can figure out the relationship between $18$ and $36$, then $18$ and $72$, then $18$ and $144$. With this information, it will be easier to solve for number of feet. Or, you can find the number of inches in one foot first.

$54$ is three times $18$. To find how many feet $54$ inches is, you would need to multiple $1.5$ by three, since $1.5$ is equal to $18$ inches. Use this information to help you with the rest of the problem.