Egyenletrendszer megoldása behelyettesítéses módszerrel?

a firstEquation listában 3.0,1.0,-1.0 van a secondEquation listában 2.0,-3.0,-19.0 .

public List<Double> getCrossingPoint(List<Double> firstEquation, List<Double> secondEquation) {

double x1 = firstEquation.get(0);

double y1 = firstEquation.get(1);

double r1 = firstEquation.get(2);

double x2 = secondEquation.get(0);

double y2 = secondEquation.get(1);

double r2 = secondEquation.get(2);

List<Double> result = new ArrayList<>();

List<Double> temp = new ArrayList<>();

temp.add(x1);

temp.add(-y1);

temp.add(r1);

double resultY = ((temp.get(0) * r2) - (x2 * temp.get(2))) / ((x2 * temp.get(1)) + (temp.get(0)*y2));

double resultX = (r1 - (y1*resultY)) / x1;

result.add(resultX);

result.add(resultY);

System.out.println("metszespont = "+resultX+ " / "+resultY);

return result;

}