Solution: Suppose there are X boys in the sixth grade of Heping Road Primary School, then there are 325-x girls.

Female students transferred out (325-x)/20 people

Boys transfer to 15, and then:

15-(325-x)/20=6

x= 145

Now there are boys145+15 =160.

Answer: Boys in grade 6 of Heping Road Primary School 160.

I hope it will help you, hope to adopt it, thank you ~