Answer
The atmosphere of Venus is 39 times thicker than that of Earth.
Work Step by Step
Here we use equation 14.2 $PV=NkT$ to find the desired ratio for the two planets.
$PV=NkT$
The no. of gas molecules per unit = $\frac{N}{V}=\frac{P}{kT}$
We can write,
$\frac{(\frac{N}{V})_{Venus}}{(\frac{N}{V})_{Earth}}=\frac{P_{Venus}/kT_{Venus}}{P_{Earth}/kT_{Earth}}=(\frac{P_{Venus}}{P_{Earth}})(\frac{T_{Earth}}{T_{Venus}})$
Let's plug known values into this equation.
$\frac{(\frac{N}{V})_{Venus}}{(\frac{N}{V})_{Earth}}=(\frac{9\times10^{6}Pa}{1\times10^{5}Pa})(\frac{320\space K}{740\space K})\approx39$
So, we can conclude that the atmosphere of Venus is 39 times thicker than that of Earth.