a. 12+6x=0<=> 6x=-12<=> x=-2
B.-2x+12=0<=> -2x=-12 <=>x=6
C.3x +1=7x-11<=> 3x-7x=-1-11<=> -4x=-12<=> x=3
D.2x +x +12=0
<=>3x+12=0
<=>3x=-12
<=>x=-4
E.x-5=3-x
<=>x+x=3+5
<=>2x=8
<=>x=4
F. 7-3x=9-x
<=>x-3x=9-7
<=>-2x=2
<=>x=-1
G. 5-3x=6x+7
<=>-6x-3x=7-5
<=>-9x=2
<=>x=-2/9
H.11-2x=x-1
<=>-2x-x=-11+1
<=>-3x=-10
<=>x=10/3
l. 15-8x =9-5x
<=>-8x+5x=15-9
<=>-3x=6
<=>x=-2
K.3+2x+5+2x
<=>4x=-3-5
<=>4x=-8
<=>x=-2