Since you did not include the figure with the diagram, I searched for a diagram of a question with the same wording of yours.
So, I will help you to solve the problem based on that figure. Such figure is now attached. Please, refer to it.
The turn B is the arc of a sector of circumference of radius 3 and angle 102°.
1) The first step is to caculate the full circumference of such circle.
That is 2π×radius = 2π(3) = 6π ≈ 6(3.14) = 18.84
2) The second step is to calculate the length of the arc
arc = circumference × angle of the sector / 360° = 18.84 × 102°/360° = 5.338
3) The third and final step is to use the scale to pass the units to miles:
5.338 units × 0.1 miles / unit = 0.5338 miles
Rounded to three decimals that is 0.534 miles ← answer