Solve for brainliest

Imagine a new pasture with grass growing on it. every day after the seeds have germinated, the number of blades of grass in the pasture triples. after 18 days, the entire pasture is completely covered in grass. how many days did it take for the pasture to be one-third covered in grass?

Determine whether the set of whole numbers is closed under addition. explain why the set is or is not closed. give an example.

Can someone me immediately, this is due by midnight! if you can't see the question, i'll text it to you. show the steps you took to get your answer.