A weather balloon has an absolute$-$pressure sensor attached. On the ground the sensor reads PA $=1\mathrm{.}01105$Pa$.$ At a height of h $=982$ m$,$ the sensor reads PB $=8\mathrm{.}87104$ Pa$.$

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Part $($a$)$

Assuming air is an incompressible fluid, enter an expression for an estimate of the density of air, in terms of the defined quantities and the acceleration due to gravity, g$.$

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Part $($b$)$

Calculate the density of air, in kilograms per cubic meter, assuming it is an incompressible fluid.