Let the matrix $ A = \begin{bmatrix} 40 & -29 & -11 \\ -18 & 30 & -12 \\ 26 & 24 & -50 \\ \end{bmatrix}$ have a certain complex number $p \neq 0$ as an eigenvalue. Which of the following must also be an eigenvalue of $A$?
- $p+20$
- $p-20$
- $20-p$
- $-20-p$