In accordance with the Bohr's model, the quantum number that characterises the Earth's revolution around the Sun in an orbit of radius $1.5 \times 10^{11} \mathrm{~m}$ with orbital speed $3 \times 10^4 \mathrm{~ms}^{-1}$ is [given, mass of Earth $=6 \times 10^{24} \mathrm{~kg}$]