39. There is a fraction $M$, if the numerator remains unchanged, and 6 is added to the denominator, it simplifies to $\frac{1}{6}$; if the denominator remains unchanged, and 4 is added to the numerator, it simplifies to $\frac{1}{4}$. Find $M=$ . $\qquad$
Reference answer: $11 / 60$