Answer
$5m\sqrt m-9m\sqrt {2m}$ or $(5-9\sqrt 2)m\sqrt m$
Work Step by Step
As $18=3^2\times2$ and $32=4^2\times2$, we have $\sqrt {18m^3}-3m\sqrt {32m}+5\sqrt {m^3}=3m\sqrt {2m}-12m\sqrt {2m}+5m\sqrt m=5m\sqrt m-9m\sqrt {2m}=(5-9\sqrt 2)m\sqrt m$
