Final answer:
The factor of x³ - 343 is (x - 7)(x² + 7x + 49).
Step-by-step explanation:
The given expression is x³ - 343. To find a factor, we can use the difference of cubes formula, which states that a³ - b³ = (a - b)(a² + ab + b²). In this case, a is x and b is 7. Therefore, the factor of x³ - 343 is (x - 7)(x² + 7x + 49). So, the correct option is 3) x² + 7x + 49.