Let \( \alpha \) and \( \beta \) be real numbers. Consider a \( 3 \times 3 \) matrix \( A \) such that \( A^{2}=3A+\alpha I \). If \( A^{4}=21A+\beta I \), then:
\( \alpha = 4 \)
\( \alpha = 1 \)
\( \beta = -8 \)
\( \beta = 8 \)