a. $\left \{ {{4x+3y=6} \atop {2x+y=4}} \right.$
$⇔\left \{ {{4x+3y=6} \atop {4x+2y=8}} \right.$
$⇔\left \{ {{4x+3y-(4x+2y)=6-8} \atop {2x+y=4}} \right.$
$⇔\left \{ {{y=-2} \atop {2x-2=4}} \right.$
$⇔\left \{ {{x=3} \atop {y=-2}} \right.$
b, $\left \{ {{2x+3y=-2} \atop {3x-2y=-3}} \right.$
$⇔\left \{ {{4x+6y=-4} \atop {9x-6y=-9}} \right.$
$⇔\left \{ {{4x+6y+9x-6y=-4-9} \atop {2x+3y=-2}} \right.$
$⇔\left \{ {{13x=-13} \atop {2x+3y=-2}} \right.$
$⇔\left \{ {{x=-1} \atop {2.(-1)+3y=-2}} \right.$
$⇔\left \{ {{x=-1} \atop {y=0}} \right.$
