Three solid cubes of edges 3cm, 4cm, 7cm are melted together to make a new cube. 218 cm³ of this melted material is lost in the process. The surface area of the newly formed cube is -

216 cm²

Total volume of melted material = (3)³ + (4)³ + (7)³

                                                  = 27 + 64 + 343 = 434cm³

Since 218cm³ is lost, therefore, remaining material = 434 - 218 = 216 cm³

Side of new cube = \(\sqrt[3]{216 }\) = 6 cm

Surface area = 6 × (side)²

                     = 6 × 36

                     = 216 cm²