Use synthetic division here, if you know it. Use -3 as divisor and use the coefficients 1 -2 -15 -14 -12. If there is no remainder, then x+3 is a factor of the given polynomial.
_____________________
-3 / 1 -2 -15 -14 -12
-3 15 0 42
---------------------------------
1 -5 0 -14 30
There's a non-zero remainder: 30. This means that the polynomial has the value 30 when x = -3, and that (x+3) is NOT a factor of the poly.
