Let y = (x/3) / (3/4). Y can be re-written as (x/3) * (4/3). Whenever you've got a rational expression, you can always multiply the numerator by the reciprocal of the denominator.
i think the OP knows that it can be written like that but just confused as to why you would do it. as hallsofivy said, you write it in that form so you can use L'hopital's rule.