Х : 6/7 = 1 1/6 : 3 1/2 - это пропорция
3 1/2х = 6/7 * 1 1/6 по свойству пропорции
3 1/2х = 6/7 * 7/6
3 1/2х = 1
х = 1 : 3 1/2 = 1 : 7/2
х = 1 * 2/7
х = 2/7
14 : (2/9х) = 5 : 2 1/7 14 : 2/9х = 5 : 15/7 = 5 * 7/15 = 7/3
2/9х * 5 = 14 * 2 1/7 2/9х = 14 : 7/3 = 14 * 3/7 = 42/7 = 6
10/9х = 14 * 15/7 х = 6 : 2/9 = 6 * 9/2 = 54/2 = 27
10/9х = 30 х = 27
х = 30 : 10/9 = 30 * 9/10
х = 270/10
х = 27