x+7
------------------- =
x^2+4x -21
x+7
= -------------------
(x+7)(x-3)
1
= ---------- where x is not equal -7 and 3
x - 3
answer is A. first choice
A vertical line has an undefined slope.
vertical lines are X= something
in this case it needs to intercept 9.
so it is X=9

Put it back into the equation,

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Answer:
The 3rd option is correct.
Step-by-step explanation:
This is because of an exponent rule that goes:
(xy)^z = x^z(y^z)
The whole thing gets raised to the power. Therefore only the 3rd one works (ps. if you can mark as brainliest that would be amazing, but if not that's fine)