If you still need help, here's my go:
For #7:
2(2-y) = 3x
The 2 outside the bracket multiples both the "2" and the "y":
2*2 - 2*y = 3x
4-2y=3x
2y=4-3x or 2y = -3x+4
OR -2y = 3x -4
Either way it becomes:
y = -1.5x+2
Input those numbers into "x":
y = -1.5(-4)+2
y =6+2
= 8
y = -1.5(0) + 2
y = 2
y = -1.5 (2/3) + 2 (or y = -3/2 (2/3) + 2)
y= -1 + 2
y = 1
y = -1.5 (3) + 2
y = -4.5 + 2
y = -2.5
-2.5 = -5/2
Therefore the answer is C
For #8: the formula for perimeter is 2L + 2W = P
Input what you have:
The perimeter is 30, the length is 30x and the width is x-1
2(3x) + 2(x-1)=30
6x + 2x -2 = 30
8x - 2 = 30
8x = 32
x= 4
Check: Perimeter = l + l + w + w
= 3x + 3x + x-1 + x-1
=3(4) + 3(4) + (4-1) + (4-1)
=12 + 12 + 3 + 3
=24 + 6
=30
For #9: line is y=mx+b (m is slope, b is y-intercept), rearrange:
-4x - 1/2y = 10
-1/2y = 10 + 4x
Multiply both sides by two to remove fraction from y
2(-1/2y) = 2(10 +4x)
-1y = 20+8x
Divide both sides by -1 since it has to be "y" and not "-y":
y = -20 - 8x
or y=-8x-20
Therefore the answer is -20
To check: the y-intercept is where x=0, so:
-4x-1/2y=10
-4(0)-1/2y = 10
-1/2y=10
Multiply both sides by 2 to remove fraction
-1y=20
y = -20
