(b) 87 π cm2
Radius and height of cone ABC are 6 cm and 2√7 cm respectively.
∴ Slant height of cone ABC = \(\sqrt{6^2+(2\sqrt7)^2}\)
= \(\sqrt{36+28}=\sqrt{64} = 8\) cm
∴ Curved surface area of cone ABC = π x 6 x 8 = 48π cm2
Also radius and height of cone DEF are 3 cm and √7 respectively
∴ Slant height of cone DEF = \(\sqrt{3^2+(\sqrt7)^2}\)
= \(\sqrt{9+7}=\sqrt{16} = 4\) cm.
∴ Curved surface area of cone DEF = π x 3 x 4 = 12π cm2
∴ Whole surface area of remaining solid
= Curved surface area of cone ABC + Area of base + Curved surface area of cone DEF
= 48 π + π(62 – 32) + 12π
= 48π + π(36 – 9) + 12π = 87 π cm2.