# Total pressure of a gas?

I was just obtaining the total pressure of a gas enclosed in a cubical container of side $L$.



My attempt at solving the problem:

$N$ = Total number of gas molecules

$m$ = Mass of one molecule

$V$ = Volume of container

$V_{x1}$ = Velocity of a single particle along x-axis

$V_r$ = Root Mean Square velocity of the gas

$d$ = Density of gas

 Now let $A_1$ and $A_2$ be two opposite faces of the cube,

The time taken to move from $A_1$ to $A_2$ and back to $A_1 = \frac{2L}{V_{x1}}$

Change in momentum $= 2mV_{x1}$

Force applied on $A_1$ by single particle = $\frac{dp}{dt}$ = $\frac{m(V_{x1})^2}{L}$

Forced applied on $A_1$ by n particles = $\frac{Nm(V_r)^2}{3V}$

Pressure on wall $A_1$= $d(V_r)^{2/3}$

There are six walls, total pressure = $6PA_1$

 But my book refers to $PA_1$ as the total pressure, why?