a) <=> $\left \{ {{3x+y=3} \atop {5x=10}} \right.$
<=> $\left \{ {{x=2} \atop {6+y=3}} \right.$
<=> $\left \{ {{x=2} \atop {y=-3}} \right.$
b) <=> $\left \{ {{4x+3y=6} \atop {4x+2y=8}} \right.$
<=> $\left \{ {{4x+3y=6} \atop {y=-2}} \right.$
<=> $\left \{ {{y=-2} \atop {4x-6=6}} \right.$
<=> $\left \{ {{y=-2} \atop {4x=12}} \right.$
<=> $\left \{ {{y=-2} \atop {x=3}} \right.$