The surface is 1/8 th of a sphere.

Take the electric field into its components and then consider the projection area of surface in î and j direction which will be quarter of a circle (same for both î and j).

Then we can just multiply the area of the quarter circle with the field component in that direction for both î and j.

Answer = 400(π/4) + 400(π/4) = 200π

2 Likes