Solve the System by the Addition Method A) $\{ ( 3,7 ) \}$

Multiple Choice

Solve the system by the addition method. If there is no solution or an infinite number of solutions, so state. Use set
notation to express the solution set.
- $$\left\{ \begin{array} { l } \frac { 1 } { 3 } x + \frac { 1 } { 3 } y = 1 \\\frac { 1 } { 4 } x - \frac { 1 } { 4 } y = - \frac { 9 } { 4 }\end{array} \right.$$

A) $\{ ( 3,7 ) \}$
B) $\{ ( - 3,6 ) \}$
C) $\{ ( - 4,7 ) \}$
D) no solution; $\varnothing$