How do you find the value of a variable and the lenght of it sides?

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 value of x is in the solution set of 4x - 12 s 16 + 8x? -10 -9 -8 -7

15m is what percent of 60m; 3m; 30m; 1.5 km? the last one is km not m