Two cars A and B each of mass $10^{3} \mathrm{~kg}$ are moving on parallel tracks separated by a distance of 10 m , in same direction with speeds $72 \mathrm{~km} / \mathrm{h}$ and $36 \mathrm{~km} / \mathrm{h}$. The magnitude of angular momentum of car A with respect to car B is $\_\_\_\_$ J.s.