Question

Carlos 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

Answer 1

This line doesn't look right.
"x + 10 + 4x = 10"

Answer 2

He combined like terms incorrectly, it should have been 4x instead of 5x right? or is it He did not distribute correctly

Answer 3

The previous line was
"x − 2(5 − 2x) = 10"
How would you simplify that?