Ratio of the ages of A and B is 6 : x.  A is 18 years younger to C.  After 9 years C will be 57 years old.  If the difference between the ages of A and B is same as the age of C, what is the value of x?

15.6

Present age of C = 57 - 9 = 48 years

Present age of A = 48 - 18 = 30 years

  A         B

  6    :    x         [ 6 → 30 so 1 → 5]

             ↓    

            ×5 

             5x

Now ⇒ 5x - 30 = 48

x = \(\frac{78}{5}\) = 15.6