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
