A thin flat plate of partially reflecting glass is at distance 4.27 cm from a convex mirror, focal length 9.86 cm. (Partially reflect glass lets some of the light through, so you can see through it, but also reflects light, so it creates the image as a plane mirror.) A girl stands at distance a from the glass, creating two virtual images: her image in glass acting as a mirror, and her image created by the convex mirror. Find the value of a, in cm, so the two virtual images are at the same horizontal distance from the girl.

A thin flat plate of partially reflecting glass is at distance 4.27 cm from a convex mirror, focal length 9.86 cm. (Partially reflect glass lets some of the light through, so you can see through it, but also reflects light, so it creates the image as a plane mirror.) A girl stands at distance a from the glass, creating two virtual images: her image in glass acting as a mirror, and her image created by the convex mirror. Find the value of a, in cm, so the two virtual images are at the same horizontal distance from the girl.