Solve the system by addition.?

2x - 4y = 7
8x + 4y = 18---------ADD

10x = 25
x = 5/2

10 + 2y = 9
2y = - 1
y = - 1/2

x = 5/2 , y = - 1/2

x=4 and y=2

2x – 4y = 7 ........[1]
4x + 2y = 9 ........[2]

[1] + 2*[2]
We get 10x = 25
x = 5/2
[1]: 2* 5/2 -4y = 7
y = -1/2

2x – 4y = 7 ........[1]
4x + 2y = 9 ........[2]
[2] * 2
8x + 4y = 18 .......[3]

[1] + [3]
10x = 25
x = 5/2
substitute x with 5/2 in [2]
4 * (5/2) + 2y = 9
10 + 2y = 9
2y = -1
y = -1/2

easy combine like terms and you will come up with -6y=72x=9.

the easiest way is by putting them on top of each other

2x - 4y = 7
4x + 2y = 9

now you need to get one variable to cancel out... the easiest would be the y's. so multiply the bottom equation by 2

2x - 4y = 7
8x + 4y = 18

now solve...
10x = 25
x = 2.5

fill that in either equation and solve for your y now
2(2.5) - 4y = 7
5 - 4y = 7
-4y = 2
y = - 1/2, or if you want them both decimale, - 0.5

4x -8y = 14 (multiply by 2)

4x + 2y = 9
____________(subtract)

-10y = 5
y = -1/2

4x + 2*-1/2 = 9

4x = 9 +1
x = 10/4 = 5/2

4x-8y=14
substract
-10y=5
y=-1/2
x=5/2