Answer is : 15
\(\phi=\vec{\mathrm{E}} \cdot \vec{\mathrm{A}}=(2 \hat{\mathrm{i}}+4 \hat{\mathrm{j}}+6 \hat{\mathrm{k}}) \times 10^{3} \cdot \mathrm{~A} \hat{\mathrm{j}}\)
\(
6=4 \times 10^{3} \mathrm{~A}\)
\(
\mathrm{A}=1.5 \times 10^{-3} \mathrm{~m}^{2}\)
\(
=15 \mathrm{~cm}^{2}\)