We make the left side into a "monic" polynomial. A "monic" polynomial
is one with the coefficient of the term with the greatest degree as 1.
So we divide each coefficient by 3:
In a "monic" polynomial of degree n, the coefficient of the term in
xn-1 is -1 times the sum of the roots of the polynomial.
So the sum of the roots is =
Set this equal to 6:
Edwin