Final answer:
To rewrite 40 - 8x³ using a common factor, factor out a common factor of 8 to get 8(5 - x³).
Step-by-step explanation:
To rewrite 40 - 8x³ using a common factor, we can factor out a common factor from both terms in the expression. In this case, the common factor is 8, so we can rewrite 40 - 8x³ as 8(5 - x³). Therefore, the correct option is C) 8x(5 - x²).