A thin cylindrical rod of length \( 10\,\text{cm} \) is placed horizontally on the principle axis of a concave mirror of focal length \( 20\,\text{cm} \). The rod is placed in a such a way that mid point of the rod is at \( 40\,\text{cm} \) from the pole of mirror. The length of the image formed by the mirror will be \( \frac{x}{3}\,\text{cm} \). The value of \( x \) is ______.