Resposta:

c) 21/2

d) 32/3

e) 2

f) 8/9

Explicação passo a passo:

c) x/14 = 9/12

12x = 9 . 14

12x= 126

x= 126/12 (:6)

x= 21/2

d) x/12 = 8/9

9x= 8 . 12

9x= 96

x= 96/9 (:3)

x= 32/3

e) x/4 = 9/18

18x = 9 . 4

18x = 36

x= 36/18

x= 2

f) 10/15 = (3x + 1)/ (5x - 2)

10 . (3x + 1) = 15 . (5x - 2)

30x + 10 = 75x - 30

75x - 30x = -30 - 10

-45x = -40

x= 40/45 (:5)

x= 8/9