#### Answer

$\{(0,4)\}$

#### Work Step by Step

1. y has opposite signs in the equations.
Multiplying the first equation by 3 will eliminate y.
$\left\{\begin{array}{lll}
9x & -3y & =-12\\
x & +3y & =12
\end{array}\right.$
2. ... add the equations and solve
$10x=0$
$x=0$
3. Back-substitute into one of the initial equations
$x+3y=12$
$0+3y=12$
$3y=12\qquad/\div 3$
$y=4$
4. Write the solution as an ordered pair.
Solution set: $\{(0,4)\}$