Answer:
There are a total of 12 groups to study
Step-by-step explanation:
You have 3 possible supplies for each subject and they can have 2 different king of diets. That gives you alredy 3*2 = 6 different options to study. You can divide further when you make the comparisson at the end of the month, allowing you to subdivide into two more categories: wheater their blood pressure is higher or lower.
That gives you a total of 3*2*2 = 12 groups to study.
I hope I could help you!