(1)5x-25=50
5x+25-25=50+25
5x=75
5x÷5=75÷5
x=15
(2)x+
x=12 1 2
x=123 2
x×3 2
=12×2 3
2 3
x=8
(3)
:x=3 4
:321 5
x=32×1 5
3 4
x=241 5
x×5=24×51 5
x=120