11. Given a polynomial with the degree 3. If it is divided by $\displaystyle x^2+2x-3$, the remainder is 2x + 1. If it is divided by $\displaystyle x^2+2x$, the remainder is 3x - 2. The polynomial is ....

A. $\displaystyle \frac23x^3+\frac43x^2+3x-2$

B. $\displaystyle \frac23x^3+\frac43x^2+3x+2$

C. $\displaystyle \frac23x^3+\frac43x^2-3x+2$

D. $\displaystyle x^3+2x^2+3x-2$

E. $\displaystyle 2x^3+4x^2+3x+2$

The book says that the answer is A, but I don't understand the part when they suddenly substitute f(-2) = -8, where does that come from? I tried doing it myself and got a (the coefficient of $\displaystyle x^3$) as $\displaystyle -\frac13$. Can you tell me what's wrong?