Rash K

Hi, I am an international student, working Full time as a placement student and earning 22,500. I am planning to do a part time along with the full time to earn some extra cash. Can you help me how the tax works for me in this case? I'm currently on the tax code 1257L. If I work for 15 hours a week part time which pays an hourly rate of 13 let's say. How does the tax work for me? Do I need to pay 40% on my part time? Could you please let me know how it all works and how much I would potentially have to pay in tax and national insurance etc?