Answer:
The music director can make 15 groups of performers with 6 sixth grade students and 5 seventh grade students in each group.
Explanation:
A school chorus has 90 sixth-grade students and 75 seventh-grade students.
Factor these two numbers:

Find GCF(90,75):

Now,

Therefore, the music director can make 15 groups of performers with 6 sixth grade students and 5 seventh grade students in each group.