x + y = 7
2x + y = 5
multiply 1st equation by -1, then add equations --- this is correct
multiply 2nd equation by -1, then add equations -- this is correct
multiply 1st equation by -2, then add equations -- this is correct
multiply 1st equation by 2 and 2nd equation by -1, then add -- correct
It appears all but 1 of the answer choices will work