Rational Roots theorem and synthetic division.
The possible roots to try are the negative and positive of 1,3,1/3,1/2,3/2.
You will find none of the integer values will work as roots.
Skipping any showing of the process, the roots that work are .
The First Two Divisions That Give Remainder 0:
| 12 16 -5 -3
-1/3 | -4 -4 3
|_______________________________________
12 12 -9 0
Next remove the factor of 3 to make the next synthetic division easier, but remember the factor for later.
| 4 4 -3
1/2 | 2 3
|_______________________________________
4 6 0
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Factorization will be whatever is equivalent to .