On the basis of Bohr's model, the radius of the 3 rd  orbit is

So we know the concept of bohr's orbital theory the radius of ${\mathrm{n}}^{\mathrm{th}}$ orbit is 

$\mathrm{r} = 0.53 \frac{{\mathrm{n}}^2}{\mathrm{z}}$

Where we know that 

$\mathrm{n}=$Number of orbit                        $\mathrm{z} =$ atomic number

So for  $3^{\mathrm{rd}}$ orbit the radius is 

$\mathrm{r} = 0.53\times \frac{9}{\mathrm{z}}$

So from above we know that $3^{\mathrm{rd}}$ orbit radius is $9$ times the radius of $1^{\mathrm{st}}$ orbit