Hi, I'm Mary. I'm a pupil. I usually get up at six on weekdays. I have tea and bread for breakfast. I have two friends. One is Lucy and the other is Lily. Lucy often gets up at six thirty. She likes bread and milk. But Lily likes hamburgers and tea. She doesn't like milk at all.

写出“之”在句子中的意思。

①一人虽听之，一心以为有鸿鹄将至，思援弓缴而射之。

②虽与之俱学，弗若之矣。

计算：$3\sqrt{2}-3\sqrt{2}$＝____ ．