SVP aidez moi je comprends pas! Mettre les etapes svp.

exercice 6:
a) 4x-5-2x+7=0 => 2x=-2 => x=-1 => y=-9 
reponse x=-1 et y=-9
b) 3x-8-0.2x+3=0 => 2.8x-5=0 => x=1.8 => y=-2.64
reponse x=1.8 et y=-2.64
c) (x/2)-6-(x/3)+1=0 => (x/6)-5=0 => x=30 => y=9
reponse x=30 et y=9
exercice 7:
a)3x-7>9 => x>(16/3) 
reponse ](16/3),+00[
b)5x-4<51 => 5x<55  => x<11 
reponse  ]-00,11[
c)8x-2≥20+12x => -22≥4x => (-22/4)≥x
reponse ]-00,(-22/4)]