Three infinitely long charge sheets are placed as shown in figure. The electric field at point P is :

$-\frac{2 \sigma}{\varepsilon_0} \hat{k}$

All the three plates will produce electric field at P along negative z-axis. Hence,

$\vec{E}_p =\left[\frac{\sigma}{2 \varepsilon_0}+\frac{2 \sigma}{2 \varepsilon_0}+\frac{\sigma}{2 \varepsilon_0}\right](-\hat{k})$

$=-\frac{2 \sigma}{\varepsilon_0} \hat{k}$

∴ correct answer is (b).