Verified answer

a/b = c/x

1/2 / 1/3 = 1/4 / x

invertendo

1/2 . 3/1 = 1/4 . 1/x

multiplicando

3/2 =1/4x

multiplicando cruzado

12x = 2

x = 2/12 simplificando por 2

x = 1/6

1/2........1/3

1/4....... X

X= 1/3x 1/4 // 1/2

X= 1/12//1/2

X= 1/12 x 2= 2/12= 1/6