Answer:
Step-by-step explanation:
I think the one you want is the last one, but I've never called it that.
21x^2 + 147x + x^3 + 343
x^3 + 343 is a cubic binomial. It factors into (x + 7) (x^2 - 7x + 49)
21x(x + 7) + (x + 7)(x^2 - 7x + 49)
(x + 7) [ 21x - 7x + x^2 + 49)
(x + 7) [x^2 + 14x + 49]
(x + 7) ( x+7)^2
(x + 7)^3
It's the only answer that does factor. There must be a simpler way of doing it, but this will give you the right answer.
