How high in meters must a column of glycerol be to exert a pressure equal to that of a 760-mm column of mercury? the density of glycerol is 1.26g/ml, whereas that of mercury is 13.6g/ml.

Using PV=nRT formula it should be clear that the pressure inversely proportional with the volume. Density is directly proportional to volume, make it also inversely proportional with the pressure (assuming the same mass of substance used).
The calculation would be: 760mm*13.6 / 1.26= 8203.17 mm * 1000 meter/mm= 8.2 meter