The brass scale of a barometer is correct at $\;0^{0}C\;$ and it reads 755 mm at $\;25^{0}C\;$ , Its reading at $\;0^{0}C\;$ is $\;r_{mercury} = 0.00018/^{0}C\;,r_{brass} =0.00021/^{0}C$

Question

$(a)\;751\;mm\qquad(b)\;755.2\;mm\qquad(c)\;750\;mm\qquad(d)\;757\;mm$