Bev is driving from Waterloo, ON to Marathon, ON. She has driven 312 \mathrm{~km}. She has 858 \mathrm{~km} still to drive. How much farther must she drive in order to be halfway from Waterloo to Marathon?
Answer Choices
A. 585 \mathrm{~km}
B. 273 \mathrm{~km}
C. 312 \mathrm{~km}
D. 429 \mathrm{~km}
E. 196.5 \mathrm{~km}