c) there are infinitely many solutions
Add x to the first equation to put it in standard form:
... x + y = 3
Divide the second equation by the common factor of all terms, 2, to put it in standard form:
... x + y = 3
These two equations describe the same line. Every point on the line is a solution to both equations, so there are infinitely many solutions. (We say these equations are "dependent.")