By synthetic division,
-5 | 1 -6 -42 79
. | -5 55 -65
- - - - - - - - - - - - - - - - -
. | 1 -11 13 14
[tex]\implies\dfrac{x^3-6x^2-42x+79}{x+5}=x^2-11x+13+\dfrac{14}{x+5}[/tex]
[tex]\implies x^3-6x^2-42x+79=(x^2-11x+13)(x+5)+14[/tex]
When [tex]x=-5[/tex], you're left with a remainder of 14.
