Step-by-step explanation:
The one that you highlighted is correct. The rest of the problems equal
[tex]16x {}^{10} [/tex]
While the third equation equal
[tex]2 {x}^{7} + 14 {x}^{7} = 16 {x}^{7} [/tex]
I would bring the x value to the 7th power instead of the 4th using the power of product rule.
So I would make the equation look like
[tex]x {}^{7} ( {2x}^{3} + {14x}^{3} )[/tex] which equal
16x^10
