Can someone please take the time out of their day and help me with this

Combine like terms7y^2 + 7(6y^2 − 8)

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?

S-7< 3 i need answering this problem someone asap answer