Turn the sentences into indirect speech.
He said, "I will have been writing a dictation for two hours by the time you come to my class".
He says, "I have received your letter".
He said, "My mother works here".

He said he  would have been writing a dictation for two hours by the time you came to his class.  

He says  he has received your letter.

He said that his  mother worked  there.