$a)$

$1\mu m={10}^{-6}m$

$100\mu m={10}^{-4}m$

$0,1\mu m={10}^{-7}m$

$b)$

$1nm={10}^{-9}m$

$300nm=3\cdot {10}^{-7}m$

$0,1nm={10}^{-10}m$

 

$c)$

$1km={10}^{3}m$

$100km={10}^{5}m$

$0,3km=3\cdot {10}^{2}m$