Three math classes: X, Y, and Z, take an algebra test.The average score in class X is 83.The average score in class Y is 76.The average score in class Z is 85.The average score of all students in classes X and Y together is 79.The average score of all students in classes Y and Z together is 81.What is the average for all the three classes?

• A. 81
• B. 81.5
• C. 82
• D. 84.5