In the text, it was shown that $N / V=2.68 \times 10^{25} \mathrm{m}^{-3}$ for gas at STP. (a) Show that this quantity is equivalent to $N / V=2.68 \times 10^{19} \mathrm{cm}^{-3},$ as stated. (b) About how many atoms are there in one $\mu \mathrm{m}^{3}$ (a cubic micrometer) at STP?