It's unfortunate they won't shell out $25 for a YEAR of basic membership of something that has the potential of helping you with your thinking skills.
If you are old enough, I would suggest getting a job. I did the day I turned 16 and it was great being able to decide what I can and can't have.
Anyway.
There are free sites that offer tactics puzzles for free. I'm not sure of the names. But I'm sure someone will come along shortly and post some links.
there is a bad side of chess.com cuz im free membership & i have limited access to tactics and puzzles etc. and my parents wont pay for gold,premium or diamond memberships.Its OUTRAGEOUS!!