Classes A and B hold a competition. The number of people in class B is twice that of class A. The average score of class A is 90 points. If the average score of the two classes is 86 points, what is the average score of class B?
甲乙两班举行比赛，乙班人数是甲班的二倍，甲班的平均成绩是90分，若两班的平均成绩为86分，则乙班的平均成绩为多少分．
<result>84</result>