What does Esther 7:9 mean?

One of the king's servants, Harbona, said, 'Look, there's a gallows seventy-five feet tall at Haman's house. He built it for Mordecai, the man who saved your life.' The king said, 'Hang him on it.' Esther 7:9 - Modern Text Bible

(Harbona points out Haman’s own gallows, and the king orders Haman to be executed on it—a poetic justice.)