A​ student's course grade is based on one midterm that counts as ​% of his final​ grade, one class project that counts as ​% of his final​ grade, a set of homework assignments that counts as ​% of his final​ grade, and a final exam that counts as ​% of his final grade. His midterm score is ​, his project score is ​, his homework score is ​, and his final exam score is . What is his overall final​ score? What letter grade did he earn​ (A, B,​ C, D, or​ F)? Assume that a mean of 90 or above is an​ A, a mean of at least 80 but less than 90 is a​ B, and so on.