Ineed the answer plz ! i’m failing

These question are hard can you me with answers

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?

The square pyramid has a volume of 441 cubic inches. what is the value of x? 1/7x is the height x is the base