Can someone explain this to me

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?

What is the square root of 45? (step by step working plz)

To decrease an amount by 16% what single multiplier would you use