smc

The volume of a cone is $\frac{1}{3}\cdot \pi \cdot r^2\cdot h$ where $r$ is the base radius and $h$ is the height. The water completely fills up the cone so the volume of the water is $\frac{1}{3}\cdot 18\cdot 144\pi =6\cdot 144\pi$. The volume of a cylinder is $\pi \cdot r^2\cdot h$ so the volume of the water in the cylinder would be $24\cdot 24\cdot \pi \cdot h$. We can equate these two expressions because the water volume stays the same like this $24\cdot 24\cdot \pi \cdot h=6\cdot 144\pi$. We get $4h=6$ and $h=\frac{6}{4}$. So the answer is $\boxed{1.5}.$