>>307
54 = 2*3^3
16 = 2^4

だから
54^(1/3) = 3 ( 2^(1/3))
16^(1/3) = 2 (2^(1/3))

54^(1/3) + 16^(1/3) - 2^(1/3) = 4 (2^(1/3))