Answer:
[tex]r = 7\ km[/tex]
Step-by-step explanation:
The formula for the area of a circle is:
[tex]A = \pi r^2[/tex]
Since we know that a semicircle is half of a circle, we can say the area is:
[tex]A = \frac{1}{2}\pi r^2[/tex]
From here solve for r:
[tex]76.97 = \frac{1}{2}\pi r^2\\153.94 = \pi r^2\\\frac{153.94}{\pi} = r^2\\r = \sqrt{\frac{153.94}{\pi}}\\r = 7[/tex]
