I am so lost on this question. I cannot figure out how to determine the effective annual return on this card.The question reads.

Baker BaseballCards, Inc. originally purchased the rookie card ofHammerin' Hank Aaron for $ 20.00$20.00. After holding the card for 33 years, Baker Baseball Cards auctioned the card for $ 80.00$80.00. What are the holding period return and the simple annual return on thisinvestment?

I understand how to figure out the holding period return = 300%

and Simple annual return = 100%

but for the life of me I do not know how to get the effective annual return on the card.

The formula is said to be EAR= (1+HPR)1/n -1

I just do not get how to figure out the (n) in the formula. If anyone could please explain this formula to me, and what I can use to compute it, I would really appreciate it.