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



cant understand what they have done. any help

Leave what they have done look at this. @Aswin24 asked the same doubt a few days ago.

Doubt from Physics

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