Sure. I'll assume you are familiar with the derivation and implications of the Gibbs function.
We know that Gibbs free energy represent a maximization of the work, since all systems tend to minimize free energy. This being said, let's assume the air bag, after combustion, returns to ambient conditions. Therefore, we are removing all the heat and work from the system and using these in the most useful way, i.e. entropy generated will be zero. However, we still need to consider the entropy at the ambient conditions, since entropy is typically defined from a reference point of 0 K.
We know that the maximum work is equal to \[W = G_R^o - G_P^o\]
From a handle table found here:courses.chem.indiana.edu/c360/documents/thermodynamicdata.pdf
We can see that \[g_f^o = 93.8 \left [ {\rm kJ \over kmol} \right]{\rm ~ for ~NaN_3}\]\[g_f^o = 0 \left [ {\rm kJ \over kmol} \right]{\rm ~ for ~Na~ and~ N_2}\]
From dimensional analysis, we can observe that, \[26.2 [{\rm g]~ NaN_3} = 0.4 [{\rm kmol]~ NaN_3}\]Therefore, the maximum work is \[W = 0.4*93.8\]