Answer
12.6 cm.
Work Step by Step
The pressure at the top surface is atmospheric pressure.
The pressure at the interface where the fluids meet must be the same on each side. Equate the expressions for the pressure at a certain depth for both liquids.
$$P_o+\rho_{alcohol}g\Delta h_{alcohol}= P_o+\rho_{water}g\Delta h_{water}$$
$$ \rho_{alcohol}\Delta h_{alcohol}= \rho_{water}\Delta h_{water}$$
$$ \Delta h_{water}=\Delta h_{alcohol}\frac{\rho_{alcohol}}{ \rho_{water}}$$
$$ =(16.0cm)(0.79)=12.6cm$$
