4: x+7=36 x+43=92 29+y=35 y=69+31 x=36-7 x=92-43 y=35-29 y=100
x=27 x=49 y=6
5. x+5=32 x-12.4=23.6
x=32-5 x=23.6+12.4
x=27 x=36
3x=120 x-400=1800
x=120÷3 x=1800+400
x=40 x=2200
6. (1) 90×2
(2) x×2