You used the formula $\displaystyle{V}=\pi{{r}}^{{2}}{h}\usepackage{cmbright}\Huge\$ to find the volume, but this is the formula for a cylinder. Note that $\displaystyle{V}=\frac{{1}}{{3}}\pi{{r}}^{{2}}{h}\usepackage{cmbright}\Huge\$ is the correct formula for a cone.