Answer:
8[tex]\pi[/tex] miles or 25.133 miles
Step-by-step explanation:
your radius is 4 miles.
The area of a circle is A= [tex]\pi r^{2}[/tex]
Therefore, the area of this circle is [tex]4^{2} \pi[/tex], or 16[tex]\pi[/tex]
Half of this area, because what you're looking for is a semi-circle, is:
8[tex]\pi[/tex] (exact) or 25.133 (rounded) miles.