The answer depends on what the 19.4 km refers to: the radius, the circumference or something else. Since you have not bothered to share that crucial bit of information, I cannot provide a more useful answer.
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A circle with a radius of 0.9 km has an area of 2.54 square km
Circumference = pi*diameter = 5.65 km, approx.
radius = 48/2 = 24 km
half of d
It would be 2.5434 km2.