Hola, necesito ayuda?

A)

12 / x = (6 / 4)(24 / 15) = = = = = simplificamos

12 / x = (3 / 2)(24 / 15)

12 / x = (3)(12 / 15)

12 / x = (12 / 5)

aplicamos la siguiente ley (1)

A / B = C / D

(A)(D) = (B)(C)

Entonces

(12)(x) = (12)(5)

x = (12)(5) / 12

x = 5

B)

1 / x = (10 / 18)(30 / 25) simplificamos

1 / x = 2 / 3 aplicamos la ley (1)

(2)(x) = 3

x = 3 / 2

c)

10 / 25 = (14 / x)(15 / 21) simplificamos

2 / 5 = (2 / x)(5)

2 / 5 = 10 / x ley (1)

(2)(x) = (5)(10)

x = 25

D)

5 / x = (5 / 16)(24 / 40)(10 / 3) simplificamos

5 / x = (1 / 2)(1 / 4)(5)

5 / x = 5 / 8

(x)(5) = (5)(8)

x = 8

suerte.