X: (6*10) =128-68 12-40: c=4 (30-y) : 2=92 20(x: 9)=4

1)×:(6*10)=128-68
×:60=60
×=60*60
×=3600
2)12-40:с=4
40:c=12-4
40:c=8
c=40:8
c=5
3)(30-y):2=92
30-y=92*2
30-y=184
y=30-184
y=-154
20(x:9)=4
x:9=20:4
x:9=5
x=5*9
x=40