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