Answer:
Number of girls in PE class is 20
D. 20 girls
Explanation:
We are given
Number of girls in 6th grade =120
Number of boys in 6th grade =102
so, firstly we will find ratios of girls and boys

now, we have
17 boys are in the first PE class
Let's assume number girls in PE class as 'x'
we know that
ratios of boys and girls must be equal
so, we get

now, we can solve for x



So,
Number of girls in PE class is 20