I am having trouble coming up with the number for n :

Lisa will invest some money on July 3, her sixteenth birthday, at 4.5% per year, compunded monthly. How much should she invest if she wants to have $ 10,000 on the November 3 following her eighteenth birthday?

I have found

P= 10,000

i= 0.045/12= 0.00375

n= ? ( not sure how to get this)

Thank you for the help