consider the arrangement to be combination of plano convex lens and a concave mirror

let \(R\) be radius of curvature

\(f_{\text {leass }}=\frac{R}{2}\) and \(f_{\text {mirror }}=\frac{R}{2}\)

first image is formed by lens

\(\frac{1}{v}-\frac{1}{u}=\frac{1}{f}\)

\(\frac{1}{v}+\frac{1}{R}=\frac{2}{R}\)

\(v=R\)

now this serves as virtual image for mirror

\(u=+R\)

\(\frac{1}{v}+\frac{1}{u}=\frac{1}{f}\)

\(\frac{1}{v}+\frac{1}{R}=\frac{-2}{R}\)

\(v=\frac{-R}{3}\)

this again serves as virtual image for the lens

\(u=\frac{R}{3}\)

\(\frac{1}{v}-\frac{1}{u}=\frac{1}{f}\)

\(\frac{1}{v}-\frac{3}{R}=\frac{2}{R}\)

\(v=\frac{R}{5}\)

hence the image is real and formed between \(O\) and \(C\)