writing test

i am applying for summer internships and have made it two a second interview and now need a writing test. generalizing, i must write a mock letter to a consulting client detailing the results of tests and further action. it is nitrates. i am looking for references or like templates i can read up on. i am feeling a little overwhelmed, and want to prove myself. i don't have a great GPA due to dropping out early in school, and realize that makes me not look great on paper.