I don't know how to express my anger. Last night, I emailed you to help me with my assignment, which is all my hope on you. However, I didn't get your reply until this morning. You even told me you can give me a hand in the afternoon. Yet I have handed in. You really made me disappointed.
I am sorry that I could not help you. I am very busy recently, so that I don't have enough to help you. But you should complete your assignment on your own. You can't always expect other people's help. You have grown up, and have to learn to deal your own business. I beg your pardon.
I didn't see your letter last night because I have something to do. When I see your letter, it was very late. But I am very sorry that I still have emergency to do. How is your assignment? If you have some problem, you can discuss with me. I will do my utmost to help you. If you have something that need me to help you later, you should tell me early, then I can arrange it on time. I also hope this thing doesn't happen again. Wish your assignment can be affirmed by your teacher.