0.6x-0.3y=-1.5
0.04x-0.02y=-0.1

6x - 3y = -15; /* 2 =>    12x - 6y = -30;
4x - 2y = -10; /*(-3) => -12x + 6y = 30
                                   
                            => 0 = 0 True, for every x and every y real numbers;

the solution is {(x, 2x + 5) / x∈R };