Recall the formula of liquid pressure due to column in terms of density of the liquid, the height of the liquid column, and the acceleration due to gravity, $P=h\rho g$

$\Rightarrow 76 \mathrm{cm}\times {\rho }_{\mathrm{Hg}}\times g=h\times {\rho }_{\mathrm{L}}\times g$

$\Rightarrow h=76 \mathrm{cm}\times \frac{{\rho }_{Hg}}{{\rho }_L}$$=76 \mathrm{cm}\times \frac{13600}{760}$$=13.6 \mathrm{m}$.