"Three boys" in Engpsh can be written as "three boys" or "3 boys".
It comes from the Engpsh language, where "three" is a number word used to count objects or people, and "boys" is a noun meaning male children or young men.
Here are some examples with Engpsh and Chinese translations:
"I saw three boys playing soccer in the park."
"我在公园里看到三个男孩在踢足球。"
"Three boys were arrested for shoppfting."
"三个男孩因偷窃被逮捕。"
"My younger brother and his friends are three boys."
"我的弟弟和他的朋友们是三个男孩。"