Question

a/b=c/d=k , 3a-4c/36-12d=k/3, b=? ​

Answer 1

$\frac{a}{b} = \frac{c}{d} = k \\ \frac{3a - 4c}{36 - 12d} = \frac{k}{3} \\ \frac{3a - 4c}{3(12 -4 d)} = \frac{k}{3} \\ \frac{3a - 4c}{12 - 4d} = k \\ \frac{3a - 4c}{12 - 4d} = \frac{c}{d} \\ 3ad - 4cd = 12c - 4cd \\ ad = 4c \\ ad = cb \\ = > cb = 4c \\ b = 4.$