Find the general solution of the system whose augmented matrix is given below. [Start 3 By 4 Matrix 1st Row 1st Column 3 2nd Column negative 7 3rd Column 5 4st Column 0 2nd Row 1st Column 12 2nd Column negative 28 3rd Column 20 4st Column 0 3rd Row 1st Column 9 2nd Column negative 21 3rd Column 15 4st Column 0 EndMatrix ]