Answer
One common solution $\Rightarrow$ $(3,-3)$
Work Step by Step
We use the addition method below:
We add the 2 equations:
$12x+5y=21$
$13x+6y=21$
Multiply both sides of the 1st equation by $13$ and the 2nd equation by $-12$ to cancel $x$:
$+156x+65y=+273$
$\underline{-156x-72y=-252}$
$-7y=21$
Solve for $y$:
$y=\frac{21}{-7}=\frac{3}{-1}=-3$
Substitute into any of the 2 equations and solve for $x$:
$12x+5y=21$
$12x+5(-3)=21$
$12x-15=21$
$12x=21+15$
$12x=36$
$x=\frac{36}{12}$
$x=3$
