Question

2a+3(a+b)-12=3(a+3b)
3(a+b)=18-2(a-3b)

Answer 1

2a+3(a+b)-12=3(a+3b) ====> 2a+3a+3b-12=3a+9b ====> 2a-6b=12

3(a+b)=18-2(a-3b) ====> 3a+3b=18-2a+6b ====> 5a-3b=18

$\left \{ {{2a-6b=12} \atop {5a-3b=18}} \right.$

$\left \{ {{2a-6b=12} \atop {-10a+6b=-36}} \right.$

2a-10a=12-36 ==> -8a=-24 ==> a=3

2*3-6b=12 ==> 6-6b=12 ==> -6b=6 ==> b=-1

P(3,-1)