1. Solve the following system of equations using the method of GaussJordan elimination.(25%) \[ x_1 + x_2 + 2x_3 + 6x_4 = 11 \]
\[ 2x_1 + 3x_2 + 6x_3 + 19x_4 = 36 \]
\[ 3x_2 + 4x_3 + 15x_4 = 28 \]
\[ x_1 - x_2 - x_3 - 6x_4 = -12 \]