( x - 80 ):40=640 , (x-80)×40=640 , x-80= 640:40, x-80= 640×40 4класс

1) (x-80):40=640
x-80=640×40
x-80=25600
x=25600+80
x=25680
2) (x-80)×40=640
40x-3200=640
40x=640+3200
40x=3840
X=96
3) x-80=640:40
x-80=96
x=176
4) x-80=640×40
x-80=25600
x=25680