(1)5x-
1
4 ×8=10,
5x-2+2=10+2,
5x÷5=12÷5,
x=2.4;
(2)12x+1.5=5.1,
12x+1.5-1.5=5.1-1.5,
12x÷12=3.6÷12,
x=0.3;
(3)5.5x-1.3x=12.6,
4.2x=12.6,
4.2x÷4.2=12.6÷4.2,
x=3;
(4)5(x-2.8)=140,
5(x-2.8)÷5=140÷5,
x-2.8=28,
x-2.8+2.8=28+2.8,
x=30.8.
(1)5x-
1
4 ×8=10,
5x-2+2=10+2,
5x÷5=12÷5,
x=2.4;
(2)12x+1.5=5.1,
12x+1.5-1.5=5.1-1.5,
12x÷12=3.6÷12,
x=0.3;
(3)5.5x-1.3x=12.6,
4.2x=12.6,
4.2x÷4.2=12.6÷4.2,
x=3;
(4)5(x-2.8)=140,
5(x-2.8)÷5=140÷5,
x-2.8=28,
x-2.8+2.8=28+2.8,
x=30.8.