Answer:
She is engaging in the explanation method of informing.
Step-by-step explanation:
The explanation as an informative method can be seen when the speaker is explaining how something works, how something is done, or what is the advantage of doing a certain thing.
This method is generally used when the speech presents something difficult to understand, or when the speaker wants to show why something should or should not be done and what are the advantages and disadvantages that this situation presents.
In the question above, we can see that Sarah is explaining the advantage of recycling plastic bottles, preventing them from polluting the oceans. She explains that the advantage of recycling is that only one plastic bottle is enough to light a 60 watt lamp for six hours.