Organized list: Start with one quarter and work your way up to $4.50. Be sure to always have 25 items.
Guess and Check:
Keep an organized list of your guesses and tweek them to find an answer.
Find a Pattern:
Look at your answers and find a pattern. How many 15 cent stamps can you trade for a bunch of 25 cent stamps?
Great Extension:
If you did not know that she sent 25 items there would be 6 answers to this POW. Can you find all 6?