Can some one answer all of these questions
9) y = −8x
2x + 4y = 0
10) 6x + 7y = 20
y = 2x
11) −3x − 5y = 6
y = −3
12) 6x − 5y = 22
y = −8
13) y = 2x
3x + 3y = −18
14) y = 8x
−5x − 5y = 0
15) y = −3
−5x − 3y = 14
16) y = 3x
−3x − y = −24

For question number (9) since 2x + 4y = 0 and y = -8x, simply substitute the second equation into the first.

2x + 4y = 2x + 4(-8x) = 2x - 32x = -30x = 0

so x = 0 and y = 0

For question (10)

6x + 7y = 20 and y = 2x (substitute 2x everywhere you see y in the first equation). So

6x + 7(2x) = 20
6x + 14x = 20
20x = 20
x = 1

(now substitute 1 for x in any of the equations)
y = 2x = 2(1) = 2

So x =1 and y =2

Question (11)
 -3(x) - 5y = 6 and y = -3 so

-3(x) - 5(-3) = 6
-3x + 15 = 6
-3x + 15 - 6 = 0
15 - 6 = 3x
9 = 3x
3x = 9
x = 3 

Question (12)
 6x - 5y = 22 and y = -8

6x - 5(-8) = 22
6x + 40 = 22
6x = 22 - 40
6x = - 18
x = -18/6
x = - 3

Question (13)
3x + 3y = -18 and y = 2x
3x + 3(2x) = -18
3x + 6x = - 18
9x = -18
x = -18/9
x = -2

Question (14)
-5x - 5y = 0 and y = 8x so

-5x -5(8x) = 0
-5x -40x = 0
-45x = 0
x = 0 and y=8(0)= 0

Question (15)
-5x -3y = 14 and y = -3

-5x - 3(-3) = 14
-5x + 9 = 14
-5x + 9 -14 = 0
9 - 14 = 5x
5x = 9 - 14
5x = -5
x = -5/5 = 5 

Question (16)
-3x -y = -24 and y = 3x so

-3x -(3x) = -24
-3x -3x = -24
-6x = - 24
x = -24/-6
x = 4 and if x = 4 and y = 3x, then y = 3(4) = 12

check the calculations and make sure they are correct

Ihave, but this question is gonna probably get deleted.