How do you solve a linear equation using elimination?

Question

All I know is that your supposed to subtract or something 
x+y=1 
-2x+y=4

Answer 1

Given equations x+y = 1 ---> (1)

-2x+y = 4 ---> (2)

To eliminate the y value subtract (2) from (1).

  x+y = 1

-2x+y = 4

(+)(-)   (-)

_________

3x = -3

Divide to each side by 3.

3x/3= -3/3

x = -1

Substitute the x value in (1).

-1+y = 1

Add 1 to each side.

y-1+1 = 1+1

y = 2

Solution x = -1 and y = 2.