How to solve systems of equations using substitution? (10 points!!!!!!)

I don't understand it, and I have a quiz coming up soon. I get how to solve systems by graphing, but I'm puzzled by substituting it.

y=x+3
y=2x+4

x+2y=8
x+3y=12

y=0.5x+2
-y=-2x+4

3x+y=-8
-2x-y=6

4x=y-1
6x-2y=-3

x=5
x+y=8

3x-y=11
5y-7x=1

y=-3x+4
x=2y+6

1/2x+1/3y=6
x-y=2

x=7-2y
2x+y=

y=1.2x-4
2.2x+5=y

help!

I'll do every other one for you!

1)
y=x+3
y=2x+4 sub in (x+3) for y
x+3=2x+4 subtract x from bothsides
3 = x+4 subtract 4 from both sides
x = -1
y=x+3 sub in -1 for x
y=-1+3
y = 2

check:
2 = 2(-1) + 4
2 = -2 + 4
2 = 2

3)
y=0.5x+2
-y=-2x+4 add this one to the one above
y + -y = 0.5x+2+-2x+4
0 = -1.5x + 6
1.5x = 6
x = 6/1.5
x = 4

y=0.5(4)+2
y=2+2
y=4

check:
-4 = -2(4)+ 4
-4 = -8 + 4
-4 = -4

5)
4x=y-1 add 1 to both sides
y=4x+1
6x-2y=-3 sub in (4x+1) for y
6x-2(4x+1) = -3
6x-8x-2 = -3
-2x = -1
x = 1/2

y = 4(1/2) + 1
y = 2 + 1
y = 3

check:
6(1/2)-2(3)=-3
3 - 6 = -3
-3 = -3

7)
3x-y=11
y = 3x - 11
5y-7x=1
5(3x-11)-7x=1
15x-55-7x=1
8x=56
x = 7

y = 3x - 11
y = 3(7) -11
y = 21 - 11
y = 10

check:
5(10)-7(7)=1
50-49 = 1
1 = 1

9)
1/2x+1/3y=6 get rid of fractions, multiply both sides by 6
3x + 2y = 36
x - y = 2 multiply this by 2
2x - 2y = 4 add new first
(2x-2y) + (3x+2y) = 4 + 36
5x = 40
x = 8

x - y = 2
8 - y = 2
-y = -6
y = 6

check:
1/2(8)+1/3(6)=6
4 + 2 = 6
6 = 6

11)
y=1.2x-4
2.2x+5=y
2.2x+5 = 1.2x-4
1.0x=-9
x = -9

y=1.2(-9)-4
y = -10.8 - 4
y = -14.8

check:
2.2(-9)+5=-14.8
-19.8+5 = -14.8
-14.8 = -14.8

19.8