Question 467157
{{{A(x+1)(x+1)^2 + Bx(x+1)^2 + Cx(x+1) }}} should have been written as {{{A(x+1)^2 + Bx(x+1) + Cx}}}, and then equated to {{{5x^2+20x+6}}}.  Compare term-by-term to get the system

A + B = 5,
2A + B + C = 20,
A = 6.

==> B = -1, and C = 9.