P got married 15 years ago. Today her age is \( 1\frac{3}{5} \) times her age at the time of her marriage. At present her son's age is \( \frac{1}{5} \) of her age. What was her son's age 4 years ago as a fraction of P's age at that time?
1
\( \frac{1}{9}\)
2
\( \frac{1}{8} \)
3
\( \frac{1}{10}\)
4
\( \frac{5}{9} \)