Verified answer

1)

15 : 3 = х : 6

15 * 6 = х * 3

90 = 3х

3х = 90

х = 90 : 3

х = 30

проверка: 15 : 3 = 30 : 6;   5 = 5 - верно

..............

2)

26 : 2 = 39 : z

26 z = 2 * 39

26 z = 78

z = 78 : 26

z = 3

проверка: 26 : 2 = 39 : 3;   13 = 13 - верно