Use the remainder theorem: we can decompose the given polynomial in terms of quotient and remainder polynomials [tex]q(x)[/tex] and [tex]r(x)[/tex], respectively, such that
[tex]x^4 - 5x^3 + x^2 - 10x - 5 = (x + 3) q(x) + r(x)[/tex]
Then letting x = -3 makes the quotient term vanish, and we're left with a remainder of
[tex]r(-3) = (-3)^4 - 5\times(-3)^4 + (-3)^2 - 10\times(-3) - 5 = \boxed{250}[/tex]
