1. Learn about the Cramer's method, for example, from these lessons - Determinant of a 3x3 matrix - Co-factoring the determinant of a 3x3 matrix - HOW TO solve system of linear equations in three unknowns using determinant (Cramer's rule) - Solving systems of linear equations in three unknowns using determinant (Cramer's rule) in this site. 2. If calculating the 3x3 determinants is too boring for you (it is really boring, I agree) then find free of charge online solvers for it. Such free of charge online solvers do exist. For example, one of them is under this link https://www.algebra.com/algebra/homework/Matrices-and-determiminant/determinant-of-3x3-matrix.solver