12x-3/4=0


2) 0,8+1/4x=0

3) 0,7x+1/5=0

4)2/5-10x=0

12x-3/4=0
12x=2/4
x=3/4*1/12
x=3/48=1/16
x=1/16

2)0,8+1/4=0
0,8x=1/4
x=1/4*10/8
x=5/16

4)2/5-10x=0
10x=2/5
x=2/5:10/1
x=1/25
или
2/5-10x=0
10x=2/5
x=0,4:10
x=0,04