1)
6/12х+4/12х+3/12х=26/27
13/12х=26/27
х=26/27÷13/12
х=26/27×12/13
х=8/9
================
2)
2 1/3х=1 2/15+2 3/5
7/3х=17/15+13/5
7/3х=17/15+39/15
7/3х=56/15
х=56/15÷7/3
х=56/15×3/7
х=8/5=1 3/5
================
3)
5 3/5х=4 5/12-2 2/3
28/5х=53/12-8/3
28/5х=53/12-32/12
28/5х=21/12
28/5х=7/4
х=7/4÷28/5
х=7/4×5/28
х=5/16
===============
4)
5/18х=10 5/6-2 1/2
5/18х=65/6-5/2
5/18х=65/6-15/6
5/18х=50/6
5/18х=25/3
х=25/3÷5/18
х=25/3×18/5
х=30