9000124505

The picture shows the virtual image $y^{\prime }$ of the object $y$ as created by a concave lens. The points $F$ and $F^{\prime }$ are focal points of the lens. The distance from the lens to each of the focal points is $20\mathrm{cm}$. The object $y$ is $25\mathrm{cm}$ height and it is in the distance $50\mathrm{cm}$ from the lens. Find the height of the virtual image $y^{\prime }$.