The altitude and atmospheric density are inversely related and the atmospheric density at 1291 km is 0.51 km/m³.
The atmospheric density is decreasing with an increase in altitude, thus altitude and atmospheric density are inversely related.
In the given plot, 1291 km must be closer to the 1000 km point with the corresponding atmospheric density of 54 kg/m³.
Therefore, the altitude and atmospheric density are inversely related and the atmospheric density at 1291 km is 0.51 km/m³.
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