Two 5p stamps and nine 9p stamps.
5p
5p
9p
9p
9p
9p
9p
9p
9p
9p
9p
OR
Eleven 5p stamps and four 9p stamps.
5p
5p
5p
5p
5p
5p
5p
5p
5p
5p
5p
9p
9p
9p
9p
What about other postage costs
Are any impossible?
What about other stamp values?
Investigate!