Help with this one can’t figure it out

To solve the problem shown in the figure attached, you must apply the proccedure shown below:

 1. You have that the equation for calculate the area of a circle is:

 A=πr²

 2. You have that the formula for calculate the diameter of a circle is:

 d=2r

 Therefore, the radius is r=d/2

 where r is the radius of the circle

 3. Keeping the information above on mind, you have the correct sequence of the equations by clearing the diameter d, is shown below:

 A=π(d/2)²
 A=πd²/4
 4A=πd²
 d²=4A/π
 d√(4A/π)

 Therefore, as you can see, the answer is:

 A=π(d/2)²
 A=πd²/4
 4A=πd²
 d²=4A/π
 d√(4A/π)