Explanation :
It is given that, the density of atmosphere ( in [tex]kg/m^3[/tex] ) on a certain planet is found to decrease as altitude increases.
It implies that there is an inverse relation between the atmospheric density and altitude.
Altitude of 1,291 km lies in between point A and point B. So, the atmospheric density lies in between [tex]0.30\ kg/m^3[/tex] and [tex]0.54\ kg/m^3[/tex].
Or the density at an altitude of 1,291 km should be less than [tex]0.30\ kg/m^3[/tex] and more than [tex]0.54\ kg/m^3[/tex].
So, the atmospheric density at an altitude of 1,291 km will be approximately [tex]0.45\ kg/m^3[/tex].