Two thin metallic spherical shells of radii $20\,\text{cm}$ and $30\,\text{cm}$, 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 $300\,\text{K}$ and the outer shell at $310\,\text{K}$. If the rate at which heat flows radially through the material is $40\,\text{W}$, find the value of $\alpha$ (in units of $\text{Js}^{-1}\text{m}^{-1}\text{K}^{-1}$).