If your average score on your first six mathematics tests was $84$ and your average score on your first seven mathematics tests was $85$, then your score on the seventh test was ． 
Overseas Competition->Knowledge Point->Word Problem Modules->Average Problems ->Questions Involving Average->Questions Involving Average (ordinary type)
The total score of the first six tests was $84\times6=504$, and the total score of the first seven tests was $85\times7=595$. Therefore, the score of the seventh test equals to the difference: $595-504=91$. 