Shelly and Terrence completed a different number of tasks in a game. Shelly earned 90 points on each task. Terrence's total points were 20 less than Shelly's total. The expression below shows Terrence's total points in the game: 90x − 20

What does the factor x of the first term of the expression represent?

The total number of tasks Terrence completed
The total number of tasks Shelly completed
The sum of Shelly's and Terrence's total points
The difference between Shelly's and Terrence's total points