Letters instead of numbers - a maths puzzle

Examples in which numbers are replaced by letters is quite a popular maths puzzle.
In the game you have to guess what numbers are hidden behind the letters.
The game contains 3 levels of difficulty: one-digit, two-digit and three-digit numbers.
For the correct answer the player gets points.
Points are entered into the general table, which allows you to compare your results with the results of other players.