If you're on about us tons then it = 20
However if it's tonnes then it = 18.143695
12x - 18 - 4x -2
12x - 4x = 8x (yours 12x - 4x = 8)
-18 - 2 = -20 (yours -18 -1 = 17)
answer:
8x - 20
Let , coordinate of points are P( h,k ).
Also , k = 3h + 1
Distance of P from origin :

Distance of P from ( -3, 4 ) :

Now , these distance are equal :

Solving above equation , we get :

Hence , this is the required solution.