The student came to the conclusion that the system has infinitely many solutions, which is not correct. Describe the error was the student work being shown.
The student did not make use of the *other* equation. It is true that a single equation with two variables will have infinite solutions, but two equations with two unknowns, not always!
though the solving for "x" is correct, is only good if the substitution is done no unto itself, because that simply gives it a circular solution which will give that, but is only good if it's used on the other equation.
