"Ahu" are stone platforms on which many moai sit. There are 313 known ahu and 125 of these carry moai. The biggest, Ahu Tongariki is 220 m (720 ft), and had the most (15) and tallest moai.
When I enrolled in college at age 19, I had a total of eight years of formal classroom education. As a result, I was not comfortable with formal lectures and receiving regular homework assignments.