16.5 hours to 32.5 hours for Christmas week

Hey! Random question here. I’m a part time employee and I get 16.5 hours a week but have just gotten my roster for next week and have been given 32.5 hours. I’m wondering how the pay goes for that? Am I on my part time pay rate for the whole thing or just my usual hours then casual rates for the other extra hours? Mum believes I’ll be on casual rates for the extra hours I’m doing but I’m not sure. I tried looking through the agreement but couldn’t find where it says about a roster change for just a week.

Thanks!!