Answer:
2x+h
Explanation:
f(x+h) means that wherever there's an x in the function f(x) we plug in a x+h
we have
(x+h)²+9
Let's start with the numerator
(x+h)²+9-(x²+9)
Distribute the exponent
x²+2xh+h²+9-x²-9
Which gives us
2xh+h²
Divide the whole thing by h to give us
2x+h