A​ student's course grade is based on one midterm that counts as 20​% of his final​ grade, one class project that counts as 10​% of his final​ grade, a set of homework assignments that counts as 50​% of his final​ grade, and a final exam that counts as 20​% of his final grade. His midterm score is 63​, his project score is 89​, his homework score is 92​, and his final exam score is 77. 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