1. 2x+y=6

3x+4y=4

y=6-2x

You do this first because you need "Y" by itself. When placing the 2x on the other side it changes to a negative. If it where a negative it would change to a positive.

3x+4y=4

Then you substitute the "Y" with the 6-2x you already have.

3x+4(6-2x)=4

3x+ 24 -8x =4

This gives you a simple equation and then you solve for "X"

-5x=-20

x=4

2x+y=6

Then you substitute for "X" in one of your equations and solve for "Y"

2*4+y=6

y=-2

(X=4 Y=-2) This is your answer.