Heat And Thermodynamics

The coefficient of cubical expansion of mercury is \(0.00018 /{ }^{\circ} \mathrm{C}\) and that of brass \(0.00006 /{ }^{\circ} \mathrm{C}\). If a barometer having a brass scale were to read \(74.5 \mathrm{~cm}\) at \(30^{\circ} \mathrm{C}\), find the true barometric height at \(0^{\circ} \mathrm{C}\). The scale is supposed to be correct at \(15^{\circ} \mathrm{C}\).