Answer:
The answer would be a total of 12 weeks .
Explanation:
Because the first four test were in a total of three weeks 
so in order to find out how many weeks for 16 quizzes just multiply
4 quizzes -3 weeks 
8 quizzes -6 weeks 
12 quizzes - 9 weeks 
16 quizzes - 12 weeks 
SO just multiply 4 by 4 and multiply 4 by 3