Answer
$-2.025 Nm^{2}/C$
Work Step by Step
Electric flux $\phi$ through any surface is given as
$ \phi= E.A=EAcos\theta$
Here, $\theta=90^{\circ}+30^{\circ}=120^{\circ}$
$E=180 N/C$, $A= 0.15\times 0.15m^{2}=0.0225m^{2}$
Hence, $\phi=180 \times0.0225\times cos 120^{\circ}$
$=-2.025 Nm^{2}/C$
The negative sign shows that it is travelling into the surface.
