In the figure, a time varying non uniform magnetic field  $B=B_{0}rt$   confined in a cyclindrical region of radius $R$  is shown. Here  $\text{'}r\text{'}$  is the radial distance from the centre and  $\text{'}t\text{'}$  is time. The induced electric field strength at a radial distance $r=\frac{R}{2}$  is  $E=\frac{B_0{R}^2}{3\times K}.$ Find the value of  $\text{'}K\text{'}.$