explanation
Consider one variable as an Independent and give some value and substitute in every
equation, then get new equations in only 3 equations in 3 unknows, if the three
equations have unique solution or no solution. if the equations have unique solution
then the system of given four equations in 3 unknows has infinity solutions (one for every
independent variable value) or
no solution (if the rank of the augmented matrix is not same as the rank of the matrix)