13. The matrix to represent a system of linear equations is simply (4 -2 -7) for the first row and (0 3 5) for the second row. Note the 3rd values in each row are separate from the others if you want to solve to echelon form.

25. This one you just add up all the corresponding values and get (-12 -8) for the first row and (5 10) for the second row.

27. Simply add X to both sides and subtract the matrix on the right to get X = (6 -11)

(-8 -1)

Sorry for my terrible matrices but these are the correct answers. Let me know if you have any questions