The area of a circle is found by the equation upper a equals pi r squared . if the area a of a certain circle is 81 pi square inches, find its radius r.

We know that
area of the circle =pi*r²
where r is the radius
clear the radius r
A=pi*r²> divide by pi> r²=A/pi>square root>  r=√[A/pi]
for Area=81*pi in²
r=√[80*pi/pi]> r=√80> r=8.94 in

the answer is
the radius is 8.94 in