Then the required distance is twice the hypotenuse of a right triangle
with sides of 6 and 8. You can use Pythagoras's theorem to compute
this. Or you can observe that 6 and 8 are twice the sides of a 3,4,5
triangle so the hypotenuse you seek is 10 mile, and so the total distance
is 20 mile.
Method 2: This is a multiple choice question. Therefore do a scale diagram
and measure the distance of off the diagram.