Answer
See explanation
Work Step by Step
Firstly converting $\text{cm/s}$ to $\text{km/s}$gives :
$3.0\times 10^{10}\text{cm/s} \times \frac{1\text{ km}}{100000 \text{ cm}}= 3.0\times10^{5}\text{ km/s}$
Secondly converting $\text{km/s}$ to $\text{miles/s}$ gives:
$3.0\times 10^{5}\text{ km/s}\times \frac{1\text{ mile}}{1.60934\text{ km}} =1.864\times 10^{5}\text{ miles/s}$
Thirdly converting $\text{miles/s}$ to $\text{miles/hr}$ gives :
$\frac{1.864\times 10^5\text{ miles}}{1\text{ s}}\times \frac{3600\text{ s}}{1\text{ hr}}= 6.71\times10^{8}\text{ miles/hr}$
