Which example illustrates how insight is used to solve problems?

The choice that illustrates insight in problem-solving is indeed the example where a person suddenly laughs at a joke once they realize it is a pun. This situation demonstrates a moment of cognitive breakthrough where the individual transforms their understanding in a flash of clarity. In this case, the humor of the joke is tied to a play on words that requires a different perspective to appreciate. The realization that makes the person laugh represents an understanding that was not previously apparent, showcasing that insight often involves a sudden shift in thinking, leading to an 'aha' moment.

In contrast, the other choices do not encapsulate insight in the same manner. Recognizing a 3D toy despite hidden angles involves perceptual understanding rather than the cognitive re-evaluation typical of insight. Similarly, a teacher giving hints leading a student to the correct answer suggests a more guided process of problem-solving rather than an instance of sudden realization. Lastly, a scientist resolving a complex equation after a break implies the benefit of incubation or the subconscious processing of information rather than an immediate insight. Thus, the correct example emphasizes the sudden and transformative nature of insight in problem-solving.