Correct option is B
Given:
The father's age today = 3 times the son's age.
After 13 years, the father's age will be twice the son's age.
Solution:
Let the present age of the son be x years.
Then, the father's present age = 3x years.
After 13 years, their ages will be:
Son's age = x+13
Father's age = 3x+13
According to the given condition:
3x+13=2(x+13)
3x+13=2x+26
3x - 2x = 26 – 13
x=13
Present age of the son = 13 years.
Option (B) is right.