Two thin metallic spherical shells of radii \(20 \mathrm{~cm}\) and \(30 \mathrm{~cm}\), respectively are placed with their centres coinciding. A material of thermal conductivity \(\alpha\) is filled in the space between the shells. The inner shell is maintained at \(300 \mathrm{~K}\) and the outer shell at \(310 \mathrm{~K}\). If the rate at which heat flows radially through the material is \(40 \mathrm{~W}\), find the value of \(\alpha\) (in units of \(\mathrm{J} \mathrm{s}^{-1} \mathrm{~m}^{-1} \mathrm{~K}^{-1}\) ).

1. A \(\frac{3}{\pi}\)
2. B \(\frac{4 \pi}{3}\)
3. C \(\frac{5}{3 \pi}\)
4. D \(\frac{\pi}{2}\)