It might have been to send my application to join the Partridge Family Fan Club.
I started with the three cent purple president, which had been the price of a letter since end of WWII. I remember when the price of a letter went to four cents— a Lincoln stamp iirc, in 1960. It was a newsworthy event.
Considering inflation, 8 cents in 1971 would be equivalent to about 60 cents today.
I remember 3 cent stamps-—but I am OLD.