Mr. brown's class is collecting books for a book drive. they started with 2 books. on the first day, they had 6 books. on the second day they had 18 books. write an equation that models this situation.

a)
y = 4x + 2

b)
y = 2(3)x

c)
y = 3x + 2

d)
y = x2 + 2