We would like to prepare a scale whose length does not change with temperature. It is proposed to prepare a unit scale of this type whose length remains, say 10 cm. We can use a bimetallic strip made of brass and iron each of different length whose length (both components) would change in such a way that difference between their lengths remain constant. If α_{iron} = 1.2 x 10^{-5} / K and α_{brass} = 1.8 x 10^{-5} / K, what should we take as length of each strip?