area

The surface area of the remaining solid = Surface area of the cube - surface area of the hemisphere

                                                                         = 6a² - 3r²...................................(1)

According to the question,

          a = 2r...............................................................................................................(2)

Substituting the value of a from (2) into equation (1) we get,

Surface Area of the remaining solid = 24r² - 3r²

Compute the exact value.