The formula for volume is Length x width x height, so we must find those values. By looking at the shape, the length is 9 km, width is 9 km, and height is 3 km, and after substituting these values in the equation, we get 9 km x 9 km x 3 km. When multiplied, it equals to 243 km^3, so the answer for the volume of the solid is B) 243 km^3.
