When a vocab is alone like this with no okurigana (hiragana attached to the kanji) it usually uses its kun'yomi reading. Numbers are an exception, though, and use the on'yomi reading. You learned the on'yomi reading when you learned this kanji, so you already know that the reading for this vocab is さん.
There are three pages of these questions total.
I’m 32 years old.
Turn around three times and bark!