Twenty Thousand
numeral
When you have two ten thousands, you have twenty thousand.
にまん
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.
このぶどうは二万円もしました。
These grapes were 20,000 yen!
二万フォロワーおめでとうございます。
Congratulations on twenty thousand followers!
二万ドルかけるよ。
I will bet twenty thousand dollars.