Evaluate $2 \times 2$ Determinant $$\left| \begin{array} { c c } - 3 & 1 \\9 & 7\end{array} \right|$$

Multiple Choice

Evaluate $2 \times 2$ determinant. $$\left| \begin{array} { c c } - 3 & 1 \\9 & 7\end{array} \right|$$

A) -30
B) -20
C) 20
D) 30