Suppose that $x^3+px^2+qx+r$ is a cubic with a double root at $a$ and another root at $b$, where $a$ and $b$ are real numbers.  If $p=-6$ and $q=9$, what is $r$?

$\textbf{(A) }0\hspace{20.2em}\textbf{(B) }4$

$\textbf{(C) }108\hspace{19.3em}\textbf{(D) }\text{It could be 0 or 4.}$

$\textbf{(E) }\text{It could be 0 or 108.}\hspace{12em}\textbf{(F) }18$

$\textbf{(G) }-4\hspace{19em}\textbf{(H) } -108$

$\textbf{(I) }\text{It could be 0 or }-4.\hspace{12em}\textbf{(J) }\text{It could be 0 or }-108.$

$\textbf{(K) }\text{It could be 4 or }-4.\hspace{11.5em}\textbf{(L) }\text{There is no such value of }r.$

$\textbf{(M) }1\hspace{20em}\textbf{(N) }-2$

$\textbf{(O) }\text{It could be }-2\text{ or }-4.\hspace{10.3em}\textbf{(P) }\text{It could be 0 or }-2.$

$\textbf{(Q) }\text{It could be 2007 or a yippy dog.}\hspace{6.6em}\textbf{(R) }2007$
1. Given the cubic polynomial \(x^3 + px^2 + qx + r\) with a double root at \(a\) and another root at \(b\), we can express the polynomial as:
   \[
   (x - a)^2 (x - b)
   \]
   Expanding this, we get:
   \[
   (x - a)^2 (x - b) = (x^2 - 2ax + a^2)(x - b) = x^3 - (2a + b)x^2 + (a^2 + 2ab)x - a^2b
   \]

2. By comparing coefficients with \(x^3 + px^2 + qx + r\), we have:
   \[
   p = -(2a + b), \quad q = a^2 + 2ab, \quad r = -a^2b
   \]

3. Given \(p = -6\) and \(q = 9\), we can set up the following equations:
   \[
   -(2a + b) = -6 \implies 2a + b = 6
   \]
   \[
   a^2 + 2ab = 9
   \]

4. Solve for \(b\) in terms of \(a\) from the first equation:
   \[
   b = 6 - 2a
   \]

5. Substitute \(b = 6 - 2a\) into the second equation:
   \[
   a^2 + 2a(6 - 2a) = 9
   \]
   Simplify and solve for \(a\):
   \[
   a^2 + 12a - 4a^2 = 9 \implies -3a^2 + 12a - 9 = 0 \implies 3a^2 - 12a + 9 = 0 \implies a^2 - 4a + 3 = 0
   \]
   Factor the quadratic equation:
   \[
   (a - 1)(a - 3) = 0 \implies a = 1 \text{ or } a = 3
   \]

6. Find the corresponding \(b\) values:
   - If \(a = 1\):
     \[
     b = 6 - 2(1) = 4
     \]
   - If \(a = 3\):
     \[
     b = 6 - 2(3) = 0
     \]

7. Calculate \(r\) for each pair \((a, b)\):
   - For \(a = 1\) and \(b = 4\):
     \[
     r = -a^2b = -(1)^2(4) = -4
     \]
   - For \(a = 3\) and \(b = 0\):
     \[
     r = -a^2b = -(3)^2(0) = 0
     \]

8. Therefore, the possible values of \(r\) are \(0\) and \(-4\).

The final answer is \(\boxed{\text{It could be 0 or }-4}\)