Two thin metal strips, one of brass and the other of iron are fastened together parallel to each other. Thickness of each strip is 2 mm. If the strips are of equal length at $0^{\circ }\text{C}$, the radius of the arc formed by the bimetallic strip when heated to ${80}^{\circ }\text{C}$ is : (Coefficient of linear expansion of brass $\text{= 19}\times {\text{10}}^{-\text{6}}/°\text{C}$ and of iron $\text{= 12}\times {\text{10}}^{-\text{6}}/°\text{C}$)