66.6。 It is a happy thing for my boyfriend and sister to go to college, but giving red envelopes is usually a beautiful moral, and my boyfriend also says it is unnecessary. Just send a 66.6 yuan to show your mind. Usually 66.6 describes someone or something as powerful and persuasive, which shows that you attach great importance to his sister and can make his sister like you. On the other hand, it also helps him save face and thinks that you are good and reasonable.