It’s d, looks like you got it already! With ratios, just pay attention to not only the numbers but order of the words as well, so you can be sure the ratio follows the problem.
10x + 2y - 6 = 0
Multiply 5x + y - 3 = 0 by 2
2(5x + y - 3 = 0) = 10x + 2y - 6 = 0
5km = 5000 meters
450m+800m= 1250m
5000m-1250m= 3,750m
3 3/4 km
You would need to use the distance formula.
Distance = Sqrt((x2-x1)^2+(y2-y1)^2)
Plug in your numbers
Distance = Sqrt((12+4)^2+(12-18)^2)
Distance = 17.09