Write a method that returns your letter grade based on the "GPA" scores on two quizzes and a test. The test score counts twice as much as a quiz. The average GPA is then found (rounding DOWN) and that GPA is converted to a letter grade. For example, gradingLetters(4, 4, 3) returns a 'B' because: 4+4+2*3=14 and 14/4=3.5. Rounding down gives us 3 which is a 'B'. Note that even a GPA of 3.9 would round down to a 3.