If there are 16 girls in Trya’s class than there are 30 boys.
Step by step explanation:
If you take the original number of girls that were in the class, 8, and multiply it by 2 you will get 16.
Then take the original number of boys that were in the class, 15, and multiply that by 2 as well and you will get 30.
I hope you understand now. :)