Semiconductor Devices And Logic Gates

The number of silicon atoms per $\mathrm{m}^3$ is $5 \times 10^{28}$. This is doped with $4.5 \times 10^{21}$ atoms $/ \mathrm{m}^3$ of arsenic. The ratio of number of electrons to number of holes after doping is (take $n_i=$ number of thermally generated electrons $=1.5 \times 10^{16} / \mathrm{m}^3$ )