can someone pls help for brainlest

Answer:
6.28km
Step-by-step explanation:
Hey,
We know that the circumfrence is the perimetert of a full circle. If we want to find the perimeter of a semicircle all we have to do is find the circumfrence and then divide it by 2 since we want to know the perimeter of half the circle.
Circumfrence is equal to 2πr. Where r is the radius and since we know the radius we an solve for the circumfrence.
2(π)(1km)=2kmπ.
The problem tells us to use 3.14 for pi so let's multiply 2 by 3.14.
6.28km is the answer!