Solve the system of equations using matrices. Use the Gaussian elimination method with back-substitution.
{ x-5y-z-7
{ x=5+y-z
{ x+y+5z=23
Use the Gaussian elimination method to obtain the matrix in row-echelon form. Choose the correct answer below.
[ 1 -1 -5 |-7 ]
A. [ 0 1 1/2| 3 ]
[ 0 0 1 | 4 ]

[ 1 -5 -1 | -7 ]
B. [ 0 1 1/2| 3 ]
[ 0 0 1 | 4 ]

[ 1 -5 -1 | 1/2 ]
C. [ 0 1 3 | 1/2 ]
[ 0 0 1 | 4 ]

[ 1 -5 0 | -7 ]
D. [ 0 1 1/2| 3 ]
[ 1 0 1 | 4 ]