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 remains constant. `If `alpa_(iron = 1.2 xx 10^-5 //K` and `alpha_(brass = 1.8 xx 10^-5//K`, what should we take as length of each strip?