Please use method of substitution numbers 9;10;11;12

1.    x = 1, y = 2.

12.  x = 1, y = -3.

Step-by-step explanation:

I won't do all these for you, just the first and the last. The method is similar  for all 12.

1.

y = x + 1

x + y = 3

Substitute y = x + 1 into the second equation:

x + y = 3 so:

x + (x + 1) = 3

2x + 1 = 3

2x + 1 -1 = 3 - 1

2x = 2

x = 1.

Now substitute x = 1 into the first equation to get the value of y:

y = x + 1

y = 1 + 1

y = 2.

12.

4x = y + 7

3x + 4y + 9 = 0

Solve for y in the first equation:

4x = y + 7                Subtract 7 from both sides of the equation:

4x - 7 = y + 7 - 7

y = 4x - 7.

Now substitute  y = 4x - 7 in the second equation:

3x + 4y + 9 = 0   so:

3x + 4(4x - 7) + 9 = 0

3x + 16x - 28 + 9 = 0

19x - 19 =  0

19x - 19 + 19 = 0 + 19

19x = 19

x = 19/19 = 1.

Now substitute x = 1 in the first equation:

4x = y + 7

4*1 = y + 7              Subtract 7 from both sides of the equation:

4 - 7 = y + 7 - 7      

-3 = y.

look at the picture.

y-intercept for the function on a picture is 4 → point (0, 4).

y-intercept for the function

is for x = 0. substitute:

y-intercept is 8 → point (0, 8).