Sphere

$\frac{\text{volume of the sphere}}{\text{surface area of the sphere}}=4\text{ cm} \\~\\ \frac{\frac43\pi r^3}{4\pi r^2}=4\text{ cm} \\~\\ \frac{\frac43\not{\pi} r\cdot\not{r^2}}{4\not{\pi}\not{r^2}}=4\text{ cm} \\~\\ \frac{\frac43r}{4}=4 \text{ cm} \\~\\ \frac43r=16\text{ cm} \\~\\ r=16/\frac43\text{ cm} \\~\\r=12\text{ cm}$