Answer
$\Delta P=54.45kPa$
Work Step by Step
Choosing $1$ as the upper point and $2$ as the lower point:
$P_{1}+\rho_{oil}*g*h_{oil}+\rho_{water}*g*h_{water}=P_{2}$
$P_{2}-P_{1}=g*(\rho_{oil}*h_{oil}+\rho_{water}*h_{water})$
Solving:
$\Delta P=9.81\frac{m}{s^2}*(0.85*1000\frac{kg}{m^3}*3m+1000\frac{kg}{m^3}*3m)$
$\Delta P=54.45kPa$
