hi i am confused about a problem

$$\\\frac{7.3*10^3}{ 4.5*10^6}\\\\
=\frac{7.3}{4.5}\times \frac{10^3}{10^6}\\\\
=\frac{7.3}{4.5}\times \frac{10^3}{10^6}\\\\
=1.6\dot2\times \frac{10*10*10}{10*10*10*10*10*10}\\\\
=1.6\dot2\times \frac{1}{10*10*10}\\\\
=1.6\dot2\times \frac{1}{10^3}\\\\
=1.6\dot2\times 10^{-3}\\\\
OR\\\\
=\frac{7.3}{4.5}\times \frac{10^3}{10^6}\\\\
=1.6\dot2\times 10^{3-6}\\\\
=1.6\dot2\times 10^{-3}\\\\$$