3x+1/14=3/7 ; 98/x-9=7 ; x+3/8=10 ; 2x-1/10=3/5 .

1)
3х + 1/14 = 3/7
3х = 3/7 - 1/14
3х = 6/14 - 1/14
3х = 5/14
х = 5/14 : 3
х = 5/14 * 1/3
х = 5/42
проверка:
3 * 5/42 + 1/14 = 3/7
15/42 + 3/42 = 18/42
18/42 = 18/42

2)
98/х - 9 = 7
98 : х = 7 + 9
98 : х = 16
х = 98 : 16
х = 98/16
х = 6 2/16
х = 6 1/8
проверка:
98 : 6 1/8 - 9 = 7
98 : 49/8 - 9 = 7
98 * 8/49 - 9 = 7
2 * 8 - 9 = 7
16 - 9 = 7
7 = 7

3)
х + 3/8 = 10
х = 10 - 3/8
х = 9 8/8 - 3/8
х = 9 5/8
проверка:
9 5/8 + 3/8 = 10
9 8/8 = 10
10 = 10

4)
2х - 1/10 = 3/5
2х = 3/5 + 1/10
2х = 6/10 + 1/10
2х = 7/10
х = 7/10 : 2
х = 7/10 * 1/2
х = 7/20
проверка:
2 * 7/20 - 1/10 = 3/5
14/20 - 1/10 = 3/5
7/10 - 1/10 = 3/5
6/10 = 3/5
3/5 = 3/5