Solve the System by the Method of Your Choice $$\begin{array} { l } x + y = - 9 \\x - y = 12\end{array}$$

Multiple Choice

Solve the system by the method of your choice. Identify systems with no solution and systems with infinitely many
solutions, using set notation to express their solution sets.
- $$\begin{array} { l } x + y = - 9 \\x - y = 12\end{array}$$

A) $\{ ( 1.5 , - 10.5 ) \}$
B) $\{ ( 1.5,10.5 ) \}$
C) $\{ ( x , y ) \mid x + y = - 9 \}$
D) $\varnothing$