Answer:
The opportunity cost of playing an hour of video games is not reading 3 chapters of a book.
Explanation:
Given that Anthony can either play 4 hours of video games or read 12 chapters of a book, to determine what is Anthony's opportunity cost of playing one hour of video games, the following calculation must be performed: 
 
4 = 12 
1 = X 
1 x 12/4 = X 
12/4 = X 
3 = X 
 
Therefore, the opportunity cost of playing an hour of video games is not reading 3 chapters of a book.