The height of the mercury column in a barometer provided with a brass scale corrercted at `0^(0)C` is observed to be `74.9 cm` at `15^(0)C`. Find the true height of the column at `0^(0)C`.
`alpha_(b) = 20 xx 10^(-6 //0)C` and `gamma_(Hg) = 175 xx 10^(-6 //^(0)C)`
A. `74.82cm`
B. `79.92cm`
C. `74.12cm`
D. `72.64 cm`