Can someone answer questions 12 through 17. i am having some trouble on this unit.

12.
 y = kx
8 = -4k
so k = -2

y = -2x
y = -2 (7)
y = -14

13.

y = kx
15 = 6k
so k = 15/6 = 2.5

y = 2.5x
y = 2.5 (7)
y =17.5

14.

y = kx
3 = 9k
so k = 3/9 = 1/3

y = 1/3x
y = 1/3 (7)
y =7/3

15

y = kx
-4 = 4k
so k = -4/4 = -1

y = - x
y = - (7)
y = -7

16.
Yes. y varies directly with x

slope = (3+6)/(2+1) = 9/3 = 3

y = mx + b
-6= 3(-1) + b
 b = -6 + 3 = -3

equation y = 3x -3

17. 
Yes
slope = (2.5 - 7.5)/(-1+3) = -5/2 = -2.5

y = mx + b
7.5= -2.5(-3) + b
7.5 = 7.5 + b
so b = 0
equation

y = -2.5x

12. 
8 = k(-4)
k = -2

13.
15 = k(6) 
k = 5/2

14. 
3 = k(9)
k = 1/3

15. 
-4 = k(4)
k = -1

16. 
No, y does not vary directly with x

17. 
Yes,
y = 5x/2