Надо 12+1целая 1/5х=20 1/2+х=3 1,4+1/5х=10

12 + 6/5х = 20; | • 5;
60 + 6х = 100;
6х = -60 + 100;
6х = 40;
х = 40/6;
х = 6 4/6;
Х = 6 2/3.

1/2 + х = 3;
х = 3 - 1/2;
Х = 2 1/2.

1,4 + 1/5х = 10; |•10;
14 + 2х = 100;
2х = 100 - 14;
2х = 86;
Х = 86 : 2;
Х = 43