A point-like luminous object is 60 cm in front of a thin convex lens of focal length 30 cm. A plane mirror, perpendicular to the axis, is placed 40…

First pass: $\dfrac1v=\dfrac1{30}-\dfrac1{60}$, so the image would form $60\ \mathrm{cm}$ behind the lens ($m_1=-1$). The mirror at $40\ \mathrm{cm}$ intercepts the converging beam $20\ \mathrm{cm}$ before that point, so the reflected rays converge to a real point $20\ \mathrm{cm}$ beyond the mirror in front of it, i.e. $40-20=20\ \mathrm{cm}$ from the lens on the mirror side ($m=+1$ for the mirror). This is a real object for the second pass at $u=-20\ \mathrm{cm}$: $\dfrac1v=\dfrac1{30}-\dfrac1{20}=-\dfrac1{60}$, so the image is virtual, $60\ \mathrm{cm}$ from the lens on the mirror side, with $m_2=\dfrac vu=3$. Net magnification $m_1\cdot1\cdot m_2=-3$, magnitude $3$.