JEE Advanced 2020 Concept Recapitulation Test 4 Paper 1

In an experiment for calculation of focal length of convex lens the distance between a screen and an object is 120cm. A convex lens is placed close to the object and is moved along the line joining object and screen, towards the screen. If the ratio of magnification of two real images is 1:16 then find the focal length of the convex lens: (in cm )