One possible version:
Dear Mr.Black,
I am Li Hua from Class 1,Senior 2.I'm the monitor of the class.We'd like to invite you to give us a lecture
about English poetry at the Poetry Festival.
To help students appreciate and write poems well,our school is going to hold the Poetry Festival from April
27th to April 28th.We hope your lecture will cover the creation and appreciation of English poetry and some
differences between Chinese poetry and English poetry.I would appreciate it if you can accept our invitation.
We are looking forward to your reply.
Yours sincerely,
Li Hua