A light from a projector passes through a two-lens system, where it first passes through a concave lens that has an unknown focal length and then through a convex lens of focal length 20 cm after which the light hits a screen. Given that the distance between the light source and the concave lens is 8 cm, the distance between the convex and concave lens is 60 cm, and the distance between the convex lens and the screen is 26 cm, find the focal length of the concave lens

A light from a projector passes through a two-lens system, where it first passes through a concave lens that has an unknown focal length and then through a convex lens of focal length 20 cm after which the light hits a screen. Given that the distance between the light source and the concave lens is 8 cm, the distance between the convex and concave lens is 60 cm, and the distance between the convex lens and the screen is 26 cm, find the focal length of the concave lens