$h=2R$ $V=\frac{4}{3}\pi {{R}^{3}}$ $V=\pi {{R}^{2}}h\to 2R$ $\frac{\frac{4}{3}\pi {{R}^{3}}}{\pi {{R}^{2}}2R}=\frac{\frac{4}{3}}{\frac{2}{1}}=\frac{4}{6}=\frac{2}{3}$