Pass data from window to window

Hello,

I have a :

- window A than contain a QPlainText "TextArea1" and a "QButton "Add".
- window B than contains a QPlainText "TextArea2" and a QButton "Submit".

when i click the button "Add" in window A, the window B show up.
Now in window B, i enter a text in TextArea2 and click the buton Submit, the text should transfer to window 1::TextArea1.

how to do this?

in other words how to transfer the plaintext value from window A::TextArea2 to window B::TextArea1 on the button submit slot ?

any one could help please ?
THanks
K|Z