Finding the Height of a Heavy Oil Column in a U-Tube with Mercury and Light Oil

[Darth Frodo]

Homework Statement

U-tube has mercury of relative density 13.6. Column of light oil is poured into one limb. It is 15 cm tall and of relative density 0.78. A column of heavy oil is poured into the other limb so that it is level with the top of the light oil column. Find the height of the heavy oil column.

Homework Equations

The Attempt at a Solution

Please find attatched.
I must leave out my workings on converting Relative density to actual density.

My problem is the Y value. 3 variables 2 equations.

 

[Darth Frodo]

Ah I think I just realized, X = Y? Is that correct?