1. [tex]\left \{ {{x+3=y} \atop {y*-2=28}} \right.[/tex]
-2y=28
-y=14
y=-14
x+3=-14
x=-14-3
x=-17
2. a+b+c=-18
b=a+1
c=a+2
a+a+1+a+2=-18
3a+3=-18
3(a+1)=-18
a+1=-6
a=-6-1
a=-7
b=a+1=-7+1=-6
c=a+2=-7+2=-5
4. a+b=-150=>a=-150-b
a-b=-84=>-150-b-b=-84
-150-2b=-84
-2b=-84+150
-2b=66
-b=33
b=-33
a-33=-150
a=-150+33
a=-117