Explanation:

Let present Age of B = x years ....... (i)
Then present age of A = x + 6 years
Age of A after 4 years = x + 6 + 4 = (x + 10) years ......(ii)
Now, According to the question ratio of (ii) and (i) is 4 : 3. So,

⇒ So, present age of B = 30 years

⇒ And present age of A = 36 years
⇒ Required Ratio = (36 – 4) : (30 – 4) = 16 : 13