#### Answer

(a) The pressure at point A is $1.057\times 10^5~N/m^2$
(b) The pressure difference between point A and point B is $4400~N/m^2$
The pressure difference between point A and point C is $4400~N/m^2$

#### Work Step by Step

$P = P_0 + \rho~g~h$
$P$ is the pressure
$P_0$ is the atmospheric pressure
$\rho$ is the density of the oil
$h$ is the depth below the surface
We can find the pressure $P_A$ at point A.
$P_A = P_0 + \rho~g~h_A$
$P_A = (1.013\times 10^5~N/m^2) + (900~kg/m^3)(9.80~m/s^2)(0.50~m)$
$P_A = 1.057\times 10^5~N/m^2$
The pressure at point A is $1.057\times 10^5~N/m^2$.
(b) The pressure difference between point A and point B is $\rho~g~\Delta h$.
$\Delta P = \rho~g~\Delta h$
$\Delta P = (900~kg/m^3)(9.80~m/s^2)(0.50~m)$
$\Delta P = 4400~N/m^2$
The pressure difference between point A and point B is $4400~N/m^2$
We would find the pressure difference between point A and point C in exactly the same way, so the pressure difference between point A and point C is also $4400~N/m^2$.