A button came off.
It might be difficult for this stain to be removed.
Renting an office in the business district will be considerably expensive, but it’s important for our image and I think it will pay for itself in about a year.
This word consists of kanji with hiragana attached. Because the hiragana ends with an う sound, you know this word is a verb.
This is an intransitive verb. That means it does not take a direct object. Something comes off. Something is removed. No direct object here. That's why this verb means to come off or to be removed.
Since this word has okurigana (hiragana attached to the kanji) you know that it's probably going to be the kun'yomi reading.
Lucky for you, the kanji readings for transitive and intransitive verbs are almost always the same. Once you learn one, you know them both! This reading is the same as 取る.