A spruce forest added 2.1 mm to trunk diameter in 1 year. If radial growth is uniform, calculate the increase in cross-sectional area of a 140 mm diameter trunk in cm².
Correct: A
Original radius 70 mm, new 71.05 mm. Area change = π(71.05² – 70²) = π(5048 – 4900) = π×148 = 465 mm² ≈ 4.65 cm². Closest 4.8 cm².