Space between two concentric conducting spheres of radii $\mathrm{a}$ and $\mathrm{b}$ $(\mathrm{b}>\mathrm{a})$ is filled with a medium of resistivity $\mathrm{\rho }$ . The resistance between the two spheres will be:

The Wheatstone bridge shown in the figure below, gets balanced when the carbon resistor used as $R_1$ has the colour code (orange, red, brown). The resistors $R_2$ and $R_4$ are $80 \mathrm{\Omega }$ and $40 \mathrm{\Omega }$, respectively. Assuming that the colour code for the carbon resistors gives their accurate values, the colour code for the carbon resistor, used as $R_3$, would be