P$3$: Water flows through a Venturi meter, as shown in the figure. The pressure of the water in the pipe supports columns of water that differ in height by $43$ cm $.$ The atmospheric pressure is $101\mathrm{.}3$ kPa $,$ the specific volume of water is $0\mathrm{.}001\frac{m^3}{k}g,$ and the acceleration of gravity is $g=9\mathrm{.}8\frac{m}{s^2}.$

Does the pressure increase or decrease in the direction of flow?

Determine the difference in pressure between points a and $b,$ in kPa $.$

A$.-421\mathrm{.}4$

B$.421\mathrm{.}4$

C$.4214$

D$.4\mathrm{.}214$