The pressure exerted by a fluid column is given by the formula $P = \rho gh$, where $\rho$ is the density of the fluid, $g$ is the acceleration due to gravity, and $h$ is the height of the column , . In a barometer, the liquid column height represents the atmospheric pressure . Since both the mercury barometer and the alternative liquid barometer are measuring the same atmospheric pressure at the same location, their pressures must be equal: $P_{\text{Hg}} = P_{\text{liquid}}$ . This gives the relation $\rho_{\text{Hg}} \cdot g \cdot h_{\text{Hg}} = \rho_{\text{liquid}} \cdot g \cdot h_{\text{liquid}}$, which simplifies to $\rho_{\text{Hg}} \cdot h_{\text{Hg}} = \rho_{\text{liquid}} \cdot h_{\text{liquid}}$. Substituting the given values: $13600 \text{ kg/m}^3 \cdot 0.76 \text{ m} = 760 \text{ kg/m}^3 \cdot h_{\text{liquid}}$. Solving for the height of the unknown liquid column: $h_{\text{liquid}} = (13600 / 760) \cdot 0.76 \text{ m} = 18 \cdot 0.76 \text{ m} = 13.6 \text{ m}$.