Students are given a convex lens and a concave mirror with a 20 cm focal length each, and the teacher instructs them to determine their focal lengths by capturing an image of a faraway object. The student chose a distant tree as the object and carefully captured each branch's fine image on a screen. The distance d₁ and d₂ between the lens/mirror and the screen in the two cases and the nature of their respective sharp images are likely to be and give reason for your answer.