Question

Breann solved the system of equations below. What mistake did she make in her work?

2x + y = 5
x − 2y = 10

y = 5 − 2x
x − 2(5 − 2x) = 10
x − 10 + 4x = 10
5x − 10 = 10
5x = 20
x = 4

2(4) + y = 5
y = −3

She should have substituted 5 + 2x

She combined like terms incorrectly, it should have been 4x instead of 5x

She subtracted 10 from both sides instead of adding 10 to both sides

She made no mistake