Final answer:
To determine the number of bacteria after 9 hours, divide the total time by the doubling time, which is every 3 hours. Starting with 100 bacteria, after 3 divisions, there will be D) 800 bacteria.
Step-by-step explanation:
To determine the number of bacteria after 9 hours, we need to divide the total time by the doubling time. In this case, the doubling time is 3 hours, so there will be a total of 3 divisions in 9 hours.
Each division doubles the number of bacteria.
Starting with 100 bacteria, after the first division there will be 200 bacteria, after the second division there will be 400 bacteria, and after the third division there will be 800 bacteria.
Therefore, the correct answer is D) 800.