How do you solve using gaussian elimination or gauss-jordan elimination, #‎x_1 + 2x_2 − 4x_3 − x_4 = 7#, #2x_1 + 5x_2 − 9x_3 − 4x_4 =16#, #x_1 + 5x_2 − 7x_3 − 7x_4 = 13#?