The van der Waals equation of the state is given by
$$P_r = \dfrac{8T_r}{3v_r-1} – \dfrac{3}{v_r^2}$$
where $P_r$, $T_r$ and $v_r$ represent reduced pressure, reduced temperature and reduced molar volume, respectively. The compressibility factor at critical point $(z_c)$ is $3/8$.
If $v_r=3$ and $T_r=4/3$, then the compressibility factor based on the van der Waals equation of state is __________ (round off to $2$ decimal places).