Given problem;
A = 4 π R²
To solve for R, we have to make it the subject of the expression.
Since
A = 4 π R² , follow these steps to find R;
Multiply both sides by
A x
=
x 4 π R²
= R²
Then find the square root of both sides
√R² =
R = 
The solution is 
√7 is not a perfect square , so it's irrational
Answer is B. irrational numbers
P.S .
Keep in mind that any of non perfect square is irrational
2-gallon
bucket for 66.72