(2) The housing area of Xiaohuajia is112m2.
(3) The area of the cover of the math textbook is about 3 square decimeters.
The area of a stamp is about 6 square centimeters.
(5) The land area of China is about 9.6 million square kilometers.
The bilingual school covers an area of about 20,000 square meters, or 2 hectares.
So the answer is: kilometers, square meters, square decimeters, square centimeters, square kilometers, square meters, hectares.