The hydrostatic pressure $(P)$ on the certain depth of sea is a function of water density and the depth measured from the sea level as shown in equation below:

$P={\displaystyle \underset{a=0}{\overset{b}{}}}g*(z)dz$

where $P$ is a hydrostatic pressure in $\frac{N}{m^2},(z)$ is water density function in $k\frac{g}{m^2},z$ is depth in $m,$ and $g$ is gravitational constant $).$ If the density of water is varying with depth with the function $(z)=2\mathrm{.}0+0\mathrm{.}1z^2,$

a$.$ By using multiple$-$application Trapezoidal Rule with $n=4,$ calculate the hydrostatic pressure at the depth of $800m.$

$[10$ marks$]$

b$.$ In certain region, the density of sea water up to certain depth cannot be represented by only one water density function, but maybe two or three water density functions, propose the computational approach to calculate the total hydrostatic pressure at that region.

$[10$ marks$]$

i need the answer for b only