A rectangular aquarium of length $L = 50$ cm is divided by a wall into two compartments $1$ and $2$. In the center of the divider there is a symmetrical biconvex lens. On the rear wall of the aquarium, in the center, an arrow is drawn.

The length of the arrow is equal to $h$. If liquid is poured into compartment $1$ of the aquarium, a clear image of the arrow appears on the front wall of compartment 2. The length of the image of the arrow is $h_1 = 4.5$ mm. If the same liquid is poured into the second compartment of the aquarium, poured out of the first compartment, then on the same wall of compartment $2$ again will appear a clear image of the arrow of length $h_2 = 2$ mm.

Find the length of the arrow $h$, the refractive index $n$ of the liquid and the distance between the lens and the walls of the aquarium $D$.