Question

I solved the system of equations below. What mistake did I 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

second last line. It's meant to be 5x= 20

Answer 2

You moved the "-10" but forgot to change the sign which resulted in you subtracting the 10 and ending up with 5x=0