Then we divide both sides of the equation by pi*5 to get r^2 by itself. So 12/(pi*5) = r^2. Take the square root of both sides and we have r = sqrt( 12/(pi*5) ), which is about 0.874 meters. The diameter is double the radius, so d = 2*r = 2*sqrt( 12/(pi*5) ), which is about 1.748 meters.