could you help me write a letter!!

[luckyspringmoon@yahoo.com]

i am a student who are studying English in a international university.If i passed final exam of english course(it includes reading ,writing,speaking and listening,all of them must be 70%),i would go to university.However,my writing skill is not enought to pass.I get 63% while if i get 65%,i can use a concession pass which values 5%. So, if i want the university to consider my situation and help me can go to university in this semester.
Could you please show me how to write a persuasive letter!!!!
and could you tell me what kind of this letter?

[Tdol]

Can you identify an area of weakness that you can work on and show some improvemnt?