航空信

háng kōng xìn de yóu zī bǐ píng xìn de gāo

航空信的邮资比平信的高。

The postage for airmail is greater than that for regular mail.

yī fēng háng kōng xìn cóng zhè r jì wǎng běi jīng dà yuē yào huā duō shǎo shí jiān

一封航空信从这儿寄往北京大约要花多少时间？

How long does it take to send an airmail letter from here to Beijing?