1. The problem statement, all variables and given/known data Hello! Please, help me to learn how to solve the following task - I really have no idea how to do that. What's important is that I need an algorithm that I can apply to the equation with different values. 2. Relevant equations The initial equation: (y - z + i) mod m = x - z Meaning that the value of (x - z) is the value of the remainder after dividing (y - z + i) by m. Let me show one example with numbers, so it will be clear what I am asking about. 3. The attempt at a solution (y - 97 + 20) mod 26 = 98 - 97 According to the definition: a mod b = c, and a=c+kb Therefore in my example: c = 98 - 97 (I am not computing this difference on purpose, because it is important for me to see all values involved) a = (y - 97 + 20) b = 26 k is unknown, but also y is unknown, so I have two unknowns here. Proceeding further I get: k×26+98−97=y−97+20 How can I find both k and y? Is there a general algorithm for such equations? I will be very grateful for your help and explanation - I need to learn this. Thank you very much!