125 - (5^3 - (3x)^3) = 125 - ( 125 - 27x^3) = 125 - 125 + 27x^3 = 27x^3;
27 * (-4/3)^3 = 27 * (-64/27)=- 64
125 - (5^3 - (3x)^3) = 125 - ( 125 - 27x^3) = 125 - 125 + 27x^3 = 27x^3;
27 * (-4/3)^3 = 27 * (-64/27)=- 64