Use the dual simplex method with an artificial objective function to find a solution to the system of equations :

x1- x2 + 4x3 = 4

x1 + x2 = 2

x1 + 2x2 - 2x3 + x4 = 3

in which x1, x2, x3, x4>= 0.

hint : use row reduce to find the basic variables first and then solve by dual simplex metod