There is no attached picture, but I guess it is like the one I attached.
If so, the first thing is finding the side measure:
[tex]A_{square}=l^2 \\ l= \sqrt{A} = \sqrt{900} \;\;\Rightarrow l=30\;in[/tex]
Now, radius is half this measure: 15 in.
And circle area is:
[tex]A_{circle}=\pi r^2=\pi\cdot(15)^2\:\;\Rightarrow A_{circle}=225\pi\;in^2[/tex]
