Luke gained 7 points in each round of a game. If he played 13 rounds of a trivia game How many points did he score in the game?
In one round, Luke gains 7 points. 
In two rounds, Luke gains 7 + 7 = 14 points. 
In three rounds, Luke gains 7 + 7 + 7 = 21 points. 

Do you see a pattern? 

In thirteen rounds, Luke gains 7 + 7 + 7 + ... + 7 = 91 points.