ANSWER:
The radius is 6 inches
The diameter is 12 inches
The circumference is 12pi inches
STEP-BY-STEP EXPLANATION:
We have that the formula for the area of the circle is the following:
[tex]A=\pi\cdot r^2[/tex]Replacing the area and solving for r (radius):
[tex]\begin{gathered} 36\pi=\pi\cdot r^2 \\ r=\sqrt[]{36}=6 \end{gathered}[/tex]The diameter equals the double radius, therefore
[tex]\begin{gathered} d=2\cdot r=2\cdot6 \\ d=12 \end{gathered}[/tex]We calculate the circumference by means of the following formula
[tex]\begin{gathered} c=2\cdot\pi\cdot r \\ c=2\cdot\pi\cdot6 \\ c=12\pi \end{gathered}[/tex]