A solid cube whose edges are 12 cm each, has been cut by a plane such that the plane bisects three edges meeting at a corner. the surface area of the remaining part of cube after the small piece is removed is :A)81 + 10 root3B) 810 + 10 root 3C) 810 - 10 root 3D) 810 + 18 root3

Answer is D
Total SA before dissection.: 6a²= 864 ...(A)
Areaof the faces removed=3(1/2* 6*3)= 54 ...(B)
Area of the new open surface added after dissection to the bigger piece= Area of Equilateral triangle of side 6*2^1/2= 3^1/2*(6*2^1/2)²/4= 18*3^1/2 ...(C)
New total surface area= A-B+C