\[5^{- 9}\ :25^{- 3} = 5^{- 9}\ :\left( 5^{2} \right)^{- 3} = 5^{- 9}\ :5^{- 6} =\]
\[= 5^{- 9 - ( - 6)} = 5^{- 9 + 6} = 5^{- 3} = \frac{1}{125}\]