Trevor solved the system of equations below. what mistake did he make in his work? 2x + y = 5 x − 2y = 10 y = 5 − 2x x − 2(5 − 2x) = 10 x − 10 + 4x = 10 5x − 10 = 10 5x = 0 x = 0 2(0) + y = 5 y = 5 a he should have substituted 5 + 2x b he combined like terms incorrectly, it should have been 4x instead of 5x c he subtracted 10 from the right side instead of adding 10 to the right side d he made no mistake