Can someone explain this highschool math question to me?

Question

solve system of equation algebraically 
y=x-2 
x-2y=4 
Can someone please explain step by step?

Answer 1

y = x-2

Apply subtraction property,subtract x from each side.

y-x = x-x-2

-x+y = -2  __________ (1)

x-2y = 4  ___________ (2)

(1)+(2) ⇒ -x+y = -2

               x-2y = 4

           ____________

                  -y = 2

                   y = -2

substitute the y value in (1)

-x-2 = -2

-x = -2+2

x = 0

solution x= 0,y = -2