7th grade math I need help with this

In the surface area formula for cylinders which expressionrepresents the lateral area

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 two square pyramids are similar. find the total volume of both pyramids if the ratio of their surface areas is 9/16