Question

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

Answer 1

`V=(4)/(3)\pi r^3\ \ \ |\cdot(3)/(4)\\\\\pi r^3=(3V)/(4)\ \ \ \ |:\pi\\\\r^3=(3V)/(4\pi)\ \ \ |:r\\\\r^2=(3V)/(4\pi r^2)`

Substitute to S.A.


`S.A.=4\pi r^2=4\pi\cdot(3V)/(4\pi r^2)=(3V)/(r)`


`(S.A.)/(V)=(4\pi r^2)/((4)/(3)\pi r^3)=(3)/(r)`


`(S.A.)/(V)=1\to(3)/(r)=1\to r=3`

Answer: B