Try Rational Roots Theorem.
Possible roots to check for are -3, -1, 1, 3; and you could expect possibly to find three roots.
-3 | 1 1 -1 -3
|
| -3 6 -15
|___________________________
1 -2 5 -18
-1 | 1 1 -1 -3
|
| -1 0 1
|_________________________
1 0 -1 -2
1 | 1 1 -1 -3
|
| 1 2 1
|_____________________________
1 2 1 -2
3 | 1 1 -1 -3
|
| 3 12 33
|_______________________________
1 4 11 36
No rational zeros found. A real zero seems to be between x values of 1 and 3 but finding it or them requires an approximation method.
If you try a graphing tool, you will find a root or zero at close to . This will be the ONLY real root.