You can easily test this if you know that (6, -10) corresponds to (X, Y). Knowing this, you can:
X = 6
Y = -10
you put this into your equation:
-10 = 3*6 - 8
calculate it:
-10 = 18 - 8
-10 = 10
This is not true of course, -10 is not equal to 10. Therefore, (6, -10) is not a solution of y = 3x-8 :)
Your answer is -43/6
1/12(4+6x3)-9
=1/12(22)-9
=11/6-9
=11/6-54/6
=-43/6
I believe 900 meters your welcomes