Final answer:
Stefan will have to attend school for 9 weeks to have taken a total of 18 quizzes.
Step-by-step explanation:
To find how many weeks Stefan will have to attend school before taking a total of 18 quizzes, we can set up a proportion with the given information. We know that Stefan took 16 quizzes over 8 weeks, so the ratio of quizzes to weeks is 16/8. We can use this ratio to find out how many weeks it would take to reach 18 quizzes.
16/8 = 18/x
Cross multiplying, we get 16x = 8*18. Dividing both sides by 16, we find that x = 9.
Therefore, Stefan will have to attend school for 9 weeks to have taken a total of 18 quizzes.