It's difficult for them to get here much before seven.

　　他們很難在7點以前早早地來到這里。

　　Two plus five is seven.

　　二加五等于七。

　　You should receive a reply within seven days.

　　你會在七天之內收到答復。

　　The ticket gives you unlimited travel for seven days.

　　憑本車票在七日內可自由乘車不受限制。

　　Seven from ten leaves three.

　　10減7得3。