Solve the system of equations using matrices. Use the Gaussian elimination method with back-substitution. 3a - b - 3c = -2 2a - b + 2c= -9 a + 2b - 4c = 3 Use the Gaussian elimination method to obtain the matrix in row-echelon form. Choose the correct answer below. O A. 1 0 -12 7 O B. 0 5 7 0 1 -5 23 0 1 - 12 23 0 0 1 - 2 0 0 1 - 2 OC. 1 0 7 - 5 OD. 1 1 - 5 7 0 1 - 12 23 0 1 - 12 23 0 0 1 -2 0 0 1 - 2 The solution set is