comparing...
a3+b3=c
a2- b2=-21
and a+b=3
a-b=-7
solving a=-5
b=2
c=-117
and the expression u gave will be 124....
\hspace{-16}$If The Polynomial can be express in the form of Diff. of $\bf{2}$ cubes like\\\\ $\bf{9x^2-63x+c=(x+a)^3-(x-b)^3}$. Then $\bf{\mid a-\mid b \mid +c\mid=}$
comparing...
a3+b3=c
a2- b2=-21
and a+b=3
a-b=-7
solving a=-5
b=2
c=-117
and the expression u gave will be 124....