句中的逗號不能改成分號，并且that前也不能加連詞and，因為這是一個主從復合句，if you want a double room為條件狀語從句，that will cost you another 15為主句——主句與從句之間不能用分號，也不能用and連接。　　

表示“在第一天”，英語通常用on the first day。如：　　

There were a good few copies sold on the first day. 第一天就賣了許多本。

Instalments are payable on the last day of the month. 分期付的款可于每月最后一日交付。

that day的意思是“那天”，通常直接用作狀語，其前不用介詞。如：　　

He was ill that day. 那天他生病。

It was bitterly cold that day. 那天天氣很冷。

We weren’t in town that day. 那天我們不在城里。

She didn’t phone that day, nor the next day. 她那天沒有打電話, 第二天也沒打。