Hundred Million
numeral
The kanji and the word are exactly the same. That means they share meanings as well.
おく
The reading is the same as the one you learned with the kanji, presumably because it's normally attached onto other numbers to signify how many hundred millions of ____ there are.
このおく歯までしっかりとどく歯ブラシで、今年は五億円を売り上げました。
We sold five hundred million yen worth of this reach toothbrush this year.
あんなに小さかった子がこんなに大きくなって、今や毎年三億ドルをかせぐ大物になっているなんて、本当にしんじられないよ。
I really can't believe that little kid has gotten so big and now earns three hundred million dollars every year.
出張の領収書は全部とっておいてください。経費は二億円までなら後で精算されますので。
Please keep all the receipts from your business trip. You will be reimbursed for your business expenses later, as long as they’re under two hundred million yen.