Questions: Solve for (r). Express your answer in simplest and exact form. [ A=3 pi r^2 quad text for r>0 ] [ r= ]

Solve for \( r \) in the equation \( A = 3 \pi r^{2} \) for \( r > 0 \).

Isolate \( r^{2} \).

Divide both sides of the equation by \( 3 \pi \):
\[ \frac{A}{3 \pi} = r^{2}. \]

Solve for \( r \).

Take the square root of both sides. Since \( r > 0 \), we only consider the positive root:
\[ r = \sqrt{\frac{A}{3 \pi}}. \]

The solution for \( r \) is:
\[ \boxed{r = \sqrt{\frac{A}{3 \pi}}}. \]

The final answer is:
\[ \boxed{r = \sqrt{\frac{A}{3 \pi}}}. \]