Which of these is a unit rate?

1) 18 students in a class
2) 18 students in 18 chairs
3) 18 students in 6 rows
4) 18 students in 2 reading groups

Cam bought some used books for $4.95. he paid $0.50 each for some books and $0.35 each for the others. he bought fewer than 8 books at each price. how many books did cam buy?

Isee the amount was $90.00 then reduced to $75.00 , what is the percent ?

The length of a shadow of the building is 36m. the length of the pole, which is perpendicular to the ground, is 1.9m. the length of the pole's shadow is 1.52m. what is the height of the building?