let's bear in mind that the cylinder and the cone both have the same volume of 112 cm³, and the same radius, but different heights.
[tex]\bf \textit{volume of a cylinder}\\\\ V=\pi r^2 h~~ \begin{cases} r=radius\\ h=height\\ \cline{1-1} V=112\\ h=7 \end{cases}\implies 112=\pi r^2(7)\implies \cfrac{112}{7\pi }=r^2\implies \cfrac{16}{\pi }=r^2 \\\\\\ \sqrt{\cfrac{16}{\pi }}=r\implies \cfrac{\sqrt{16}}{\sqrt{\pi }}=r\implies \cfrac{4}{\sqrt{\pi }}=r \\\\[-0.35em] ~\dotfill[/tex]
[tex]\bf \textit{volume of a cone}\\\\ V=\cfrac{\pi r^2 h}{3}\qquad \qquad \begin{cases} r=\frac{4}{\sqrt{\pi }}\\ V=112 \end{cases}\implies 112=\cfrac{\pi \left( \frac{4}{\sqrt{\pi }} \right)^2(h)}{3} \\\\\\ 336=\pi \left( \cfrac{4^2}{(\sqrt{\pi })^2} \right)h\implies 336=\pi \cdot \cfrac{16h}{\pi }\implies 336=16h \\\\\\ \cfrac{336}{16}=h\implies \blacktriangleright 21=h \blacktriangleleft[/tex]
