A point object $O$ is placed in front of two thin symmetrical coaxial convex lenses $L _ { 1 }$ and $L _ { 2 }$ with focal length 24 cm and 9 cm respectively. The distance between two lenses is 10 cm and the object is placed 6 cm away from lens $L _ { 1 }$ as shown in the figure. The distance between the object and the image formed by the system of two lenses is $\_\_\_\_$ cm