问题详情

Tom has taken 5 of the 8 equally weighted tests in his U.S. History class this semester, and he has an average score of exactly 78.0 points. How many points does he need to earn on the 6th test to bring his average score up to exactly 80.0 points？
A.90
B.88
C.82
D.80
E.79请帮忙给出正确答案和分析，谢谢！