Exercise 3 solution

3 diopters: focal length = 1 / 3 = 0.33 m (about 33 cm).
200 mm lens with 100 mm extension: m = 100 / 200 = 0.5. That is 0.5 times, which the article places at the boundary between extreme close-up (0.5 to 1.0) and not yet macro. The strict macro definition needs 1:1 (m = 1) or greater, so no; it would need 200 mm of extension.