Ah I'm sorry you got stuck on this one. Did it work out okay today? If you google that letter, it is available online. It really is a brilliant piece of writing.
Tell that teacher you'll turn it in late. Everyone makes mistakes... but don't miss the opportunity to write about that letter.
King was a hero.. for sure, and a great writer.
For your paper, compare his assertion of a moral responsibility to disobey unjust laws with Thoreau's refusal to pay taxes when he disapproved of the government's actions. That will make a good thesis.