Number + 周
The classifier 周 (zhōu) is a measure word meaning 'week.' It is used with numbers to count weeks, as in 两周 (two weeks) or 好几周 (quite a few weeks). It is interchangeable with 个星期 but is more concise and slightly more formal.
这个项目大概需要两周才能完成。
Zhège xiàngmù dàgài xūyào liǎng zhōu cái néng wánchéng.
This project will probably take about two weeks to complete.
我已经好几周没去健身房了。
Wǒ yǐjīng hǎo jǐ zhōu méi qù jiànshēnfáng le.
I haven't been to the gym for several weeks.
他在国外待了三周就回来了。
Tā zài guówài dāi le sān zhōu jiù huílái le.
He came back after staying abroad for only three weeks.