1)5 11/14x- 8/15= 5/21
2)7 3/10+25/28x= 8 13/35
3)3 1/3- 1 1/20x=1 14/15
4)3/8x+7/12x- 5/6x=9/32

5  11/14x - 8/15 = 5/21
5  11/14x = 5/21 + 8/15
5  11/14x = 25/105 + 56/105
5  11/14x = 81/105
x=81/105 : 5  11/14x
x=81/105 : 81/14
x=81/105 * 14/81
x=14/105
x=14/105
==========================
7 3/10 + 25/28x=8  13/35
73/10 + 25/28x=293/35
25/28x=293/35 - 73/10
25/28x=586/70 -  511/70
25/28x=75/70
x=75/70 : 25/28
x=75/70 * 28/25 
x=84/70
x=1.2
==========================
3  1/3 - 1 1/20x = 1  14/15
10/3 -21/20 = 29/15
-21/20x=29/15-10/3
-21/20x=29/15 - 50/15
-21/20x=- 21/15
21/20x=21/15
x=21/15 : 21/20
x=21/15 * 20/21
x=20/15
x=4/3
x=1  1/3
================================
3/8x+7/12x-5/6x=9/32
3/8x+7/12-10/12x=9/32
3/8x-3/12x=9/32
9/24x-6/24x=9/32
3/24x=9/32
1/7x=9/32
x=9/32:1/7
x=9/32 * 7/1
x=49/32
x=1  7/32