How long hasn’t he heard from Clara?

M: Clara! How are you? I haven’t heard from you for at least three years. What are you doing?
W: I came back from Australia. Now I’ve opened a company. I heard from Miss Sue that you are getting married. Congratulations!
M: Thank you!
W: Why did you keep so quite about it?
M: I’m sorry. I mean to tell you. But I couldn’t find you by your previous address.
W: When will the wedding be?
M: January 1st
W: I want to give you a present. What would you like?
M: Let me see. Oh, a bunch of flowers will do.
W: I see. Bye.
M: Bye.