Sc. 3, lines 75–80: why are lady macbeth's words ironic? how does this create suspense? how do macduff's words in lines 75–78 ironically echo lady macbeth's speech in act i, in which she calls on the spirits of evil to "unsex her"?

1. Lady Macbeth and Macbeth were deliberating their spirits about being king and queen of Scotland after the murder. Lady Macbeth is telling that they hold his possessions in trust, ready to return it whenever he wants, but she has no plans to return it, as she plans to kill him.
2. Macduff is saying to Lady Macbeth that his news of Duncan's murder would be too much for her weak self to cope. This is ironic since Lady Macbeth telled on the spirits to "unsex her" and make her tough, unlike how a woman usually is.

Normally it is at the top left, above where the music starts.