A teardrop balloon is fully inflated to a perimeter of 25 inches by blowing into it 12 times.....?

Maybe I'm missing something here, but it seems like you would need to know how long it takes the breath to enter the balloon and how often you breathe into it. If you blow into it once, then allow it to deflate before blowing into it again, you'd never fill it more than the 8.33% a single breath would provide.