Answer :
It's hard to guess what the question is.
The quantity there apparently has the unit of 'square inches',
so it's already an area.
The quantity there apparently has the unit of 'square inches',
so it's already an area.
[tex]The\ surface\ area\ of\ the\ sphere=4 \pi r^2\\\\The\ surface\ area\ of\ the\ sphere=81 \pi (in^2)\\\\4 \pi r^2=81 \pi\\4r^2=81\ /:4\\\\r^2= \frac{\big{81}}{\big{4}} \ \ \ \Rightarrow\ \ \ r= \sqrt{ \frac{\big{81}}{\big{4}}} = \frac{\big{9}}{\big{2}}=4.5\ (in)\\\\the\ radius\ of\ the\ sphere\ is\ 4.5\ in[/tex]