Answer:
21
Step-by-step explanation:
We know that the total number of students has to be divisible by 3. So to solve this specific problem, you can either use a guess and check system, prior knowledge, or by using a factoring method.
If we try to divide all four answer choices evenly by 3, only 21 leaves us with a whole number. Therefore, there could be 21 students participating.
25/3 = 8.33
21/3 = 7
23/3 = 7.667
26/3 = 8.667