a)(x:2)×3=30×3
(x:2)×3=90
x:2=90:3
x:2=30
x=2×30
x=60
b)(7×9-x×5)-9:3=20
(7×9-x×5)-9=3×20
(7×9-x×5)-9=60
(7×9-x×5)=9+60
(7×9-x×5)=69
7×9-x×5=69
7×9-x=69:5
7×9-×=? este greseala
c)909:9-(9×9:x-9)=101
9-(9×9:x-9)=909:101
9-(9×9:x-9)=9
9×9:x-9=9-9
9×9:x-9=0
9×9:x=9+0
9×9:x=9
9:x=9×9
9:x=81
x=81:9
x=9
d)35×5-54:x×4=139
Asta incearca sa il faci tu singura.