I went to a post office and bought five postcards.
I said I would need five sheets of copy paper, not three, didn't I? Why can't you even do something this easy, Koichi?!
Sounds like a plan. I’ll give you five extra stickers as a bonus too.
You know that 枚 is a flat objects counter. So, now we're counting! You have five flat objects.
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.