Which sentence is punctuated correctly?

Question

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Deandre's science teacher did a lot of challenging experiments in class; for example, he made his students build contraptions for an egg drop from two stories high.
Deandre's science teacher did a lot of challenging experiments in class for example; he made his students build contraptions for an egg drop, from two stories high.
Deandre's science teacher did a lot of challenging experiments in class, for example, he made his students build contraptions for an egg drop, from two stories high.
Deandre's science teacher did a lot of challenging experiments; in class for example, he made his students build contraptions, for an egg drop, from two stories high.

Answer 1

The correctly punctuated sentence is:

Deandre's science teacher did a lot of challenging experiments in class; for example, he made his students build contraptions for an egg drop from two stories high.