Answer
$f(x)=\dfrac{3x^2}{x^2+7}$
Work Step by Step
An example of a function with one horizontal asymptote is
$f(x)=\dfrac{P(x)}{Q(x}$,
where $P(x)$ and $Q(x)$ have the same degree, $Q(x)\not=0$ and the coefficient of the term of highest degree in the numerator is 3 times the the coefficient of the term of highest degree in the denominator.
For example:
$f(x)=\dfrac{3x^2}{x^2+7}$
The horizontal asymptote is
$y=\dfrac{3}{1}=3$
