Imagine a tree that has a radius of 20 cm and that produces a new layer of wood 0.5 cm thick (the outer radius of the new wood is 20.5 cm and the inner radius is 20 cm). What is the cross-sectional area of the new layer of wood (CSA = pr²)? If each leaf needs 0.1 cm² of wood to supply it with water, how many leaves can the tree have? If the tree produces a new ring of wood next year that is again 0.5 cm thick, how many leaves can the tree have next year (assume that wood conducts water for only 1 year, not 2 years)?