First you need your subject. Which would be what the important assignment is. Then “Dear teacher,” but don’t say teacher, use the teachers name” then hit return twice, then ask, and be straight forward. Return twice again then “thank you,” or “sincerely,” then your name. So like this for example:
Subject
Dear Mrs. Teacher,
I need an extension on the important assignment because *state your reason and say how much longer you might need*
Thank you, your first and last name.
I just had this assignment in the beginning of the year and that’s how I did it and got it right.