Question

Help please, i don't understand it!!!!

Answer 1

$V=\dfrac{4}{3}\pi r^3\ \ \ |\cdot\dfrac{3}{4}\\\\\pi r^3=\dfrac{3V}{4}\ \ \ \ |:\pi\\\\r^3=\dfrac{3V}{4\pi}\ \ \ |:r\\\\r^2=\dfrac{3V}{4\pi r^2}$

Substitute to S.A.

$S.A.=4\pi r^2=4\pi\cdot\dfrac{3V}{4\pi r^2}=\dfrac{3V}{r}$

$\dfrac{S.A.}{V}=\dfrac{4\pi r^2}{\frac{4}{3}\pi r^3}=\dfrac{3}{r}$

$\dfrac{S.A.}{V}=1\to\dfrac{3}{r}=1\to r=3$

Answer: B