How to solve?
Here, we just have to express r in terms of x when we are provided with the relation between x and r. We have to flip and sent it to the Right hand side.
Solution:
We have,
Solving it further,

Taking 5/3 to the other side by dividing it,

Now, taking π to the other side by dividing it,

Cube rooting LHS to get r
![\large{ \longrightarrow{ \rm{ \sqrt[3]{ (3x)/(5\pi) } = r}}}](https://img.qammunity.org/2021/formulas/mathematics/high-school/skzjyt1wt9cxr60j7yrp45jh9fu6b4iq9f.png)
Flipping it,
![\large{ \longrightarrow{ \rm{r = \sqrt[3]{ (3x)/(5\pi) } }}}](https://img.qammunity.org/2021/formulas/mathematics/high-school/df4qwpk5tecwfjn833bgls9r4xswucg7s4.png)
So, the correct option:

━━━━━━━━━━━━━━━━━━━━