Answer:
4 sophomore girls .
Step-by-step explanation:
If a student's gender and class are to be independent when a student is selected at random, two conditions must be met:
n° boys = n° girls
n° freshmen = n° sophomore
Currently, there are 10 boys and 6 girls, thus 4 girls must join.
Currently, there are 10 freshmen and 6 sophomores, thus 4 sophomores must join.
Therefore, 4 sophomore girls must join.