Correct Answer - Option 4 : 25

The ratio of the present ages of A and B is 3 : 5.

Let the common multiple be x.

So, the present age of A = 3x and the present age of B = 5x.

The sum of the present ages of A and B is 40 years.

According to question:

3x + 5x = 40

8x = 40

x = 5

Age of B = 5x

= 5 × 5 = 25 years

Hence, the age of B is 25 years.