To solve an equation of the first degree on a field is not a problem since we already have a model resolution. What happens to the model resolution on a ring?
By "first degree" I assume you mean a system of linear equations? If so, then for Euclidean rings there is the Hermite canonical form of a matrix, somewhat analogous to reduced row echelon form for matrices over a field. This can be used to determine solvability and to provide solutions in solvable instances.