Three cubes of metal whose edges are 9, 12 and 21 cm respectively, are melted and one new cube is made. Find the edge of the new cube?  Choices.
A) 28
B) 22.7
C) 66
D) 18
E) 99

Rationale: "93 + 123 + 213 = a 3 = > a = 22.7 answer : b"
Answer: B