One limb of a U-tube has a cross-sectional area of $A$, whereas the other limb has a cross-sectional area of $4A$. As illustrated, the tube is filled with water of density $1000\ \text{kg m}^{-3}$ and oil of density $850\ \text{kg m}^{-3}$. In the left-hand limb, the layer of oil resting above the water has a length of $30.0\ \text{cm}$. What is the height difference $x$ between the liquid levels in the two limbs of the tube?
- A$4.5\ \text{cm}$
- B$6.2\ \text{cm}$
- C$23.8\ \text{cm}$
- D$25.5\ \text{cm}$