1) 2a+ab+(9+6)+9+6=54
6a+9b=12b
2a+2b=24
6a=3b
a+b=12
2a=b
3a=12
a=4
b=2*a=8
2) x+2y= -2
3x-8y=10
x=-2-2y
3(-2-2y)-8y=10
-6-6y-8y=10
-14y=16
y=-8/7
x=-2-2*(-8/7)
x=-2+16/7
x=2/7
3) 2x+y+9
5x-4y=3
8x+4y=36
5x-4y=3
13x=39
x=13
y=9-2x
y=9-26
y=-17
x=13 i y =-17
4) 2x+3y=4
8x-5y=-1
-8x-12y=-16
8x-5y=-1
-17y=-17
y=1
2x=4-3y
2x=1
x=1/2
x=1/2 i y=1