The correct answer is:
If you must have the same number of boys and girls in each group, you can have 7 groups.
Explanation:
To do this, we find the Greatest Common Factor (GCF) of 14 and 21. For this, we find the prime factorization of each number:
14 = 2(7)
21 = 3(7)
The only common factor between these two numbers is 7. Thus we can have 7 groups.
(In each group, we would have 14/7 = 2 boys and 21/7 = 3 girls.)