Answer:
First choice
Step-by-step explanation:
The difference quotient in general is
. To get an expression for
, replace x with x + h.
For this question,

Factor
out of the numerator.

Use the geometric mean for right triangles here. Like this

. Cross multiply to get

, and

. That simplifies down to

. Pull out the 9 as a perfect square of 3 and you're left with

, first choice above.