A thin rod of length $\large\frac{f}{3}$ is placed along optical axis a concave mirror of focal length f such that its image which is real and elongated just touches rod . calculate the magnification.

Question

$(a)\;\frac{3}{4} \\ (b)\;\frac{-3}{2} \\ (c)\;\frac{3}{2} \\ (d)\;\frac{-3}{4} $