We must calculate the volumen of the cylinder and the sphere:
Volume cylinder:
[tex]\begin{gathered} v=\pi\cdot h\cdot r^2 \\ v=3.14\cdot18\cdot6^2 \\ v=2034.72 \end{gathered}[/tex]volume sphere:
[tex]\begin{gathered} v=\frac{4}{3}\cdot\pi\cdot r^3 \\ v=\frac{4}{3}\cdot3.14\cdot15^3 \\ v=14130 \end{gathered}[/tex]the minimum number:
[tex]v=\frac{14130}{2034.72}=6.94[/tex]Therefore, the minimum number is 6.