It would help if you'd please use parentheses to indicate clearly what is to be multiplied or divided by what.
I am assuming (not claiming that I know) you meant:
(12f-16) (5)
------------ divided by --------------
16 9f^2 - 16
Factor as much as possible before attempting division:
4(3f-4) 5
--------- divided by -----------------
16 (3f-4)(3f+4)
This is equivalent to multiplying as follows:
4(3f-4) (3f-4)(3f+4)
---------- * -----------------
16 5
Is this what you meant? If so, please finish the work. If not, please copy down the original problem making liberal use of parentheses for clarity.