$x^3-9x-5=0$, then what is $x^4-18x^3-81x^2-12$ If we have $x^3-9x-5=0$, then what $x^4-18x^3-81x^2-12$ equals to?
This is a multiple choices question. 
A)$5$ B)$25$ C)$42$ D)$67$ E)$81$.
My attempt, 
By long division of polynomials, we have $x^4-18x^3-81x^2-12=(x-18)(x^3-9x-5)+(-72x^2-157x-102)$
Since $x^3-9x-5=0$, whatever $x$ could be, $x^4-18x^3-81x^2-12=-72x^2-157x-102$ 
How to proceed? 
P/S. Conclusion, NONE of the options can be right.

Simply use synthetic substitution to solve for $x$ in the first equation, then plug that value into the second.
