我昨天给老师写了一封信。

Wǒ zuótiān gěi lǎoshī xiě le yì fēng xìn.

I wrote a letter to the teacher yesterday.

桌子上有三封重要的邮件。

Zhuōzi shang yǒu sān fēng zhòngyào de yóujiàn.

There are three important letters on the table.

我给妈妈写了一封很长的信。

Wǒ gěi māma xiě le yì fēng hěn cháng de xìn.

I wrote a very long letter to my mom.