How to create a function to solve two unknowns

Trying to figure out where to start with this. The equation contains two unknowns and the solution for x or y is always a positive number.

Given a = 123 and b = 55 and c = 5. In this case x = 31 and y = 93 but I don't know that ahead of time and I'm trying to write a function in C# to solve it.

a - (x + 1) * 96 - (y + 2) + 3104 - c = b

Also if a = 30 and b = 8 and c = 19 then x = 32 and y = 35

so for: Round 1 function solveX(123, 55, 5) returns 31 function solveY(123, 55, 5) returns 93

Round 2 function solveX(30, 8, 19) returns 32 function solveY(30, 8, 19) returns 35

Any pointers on where to get started would be great.

Thanks.