$\begin{array}{l}\phantom{\phantom{;}5m^{2}+0.9;}{\phantom{;}25m^{4}\phantom{-;x^n}-\frac{22.5}{5}m^{2}\phantom{-;x^n}+\frac{4.05}{5}\phantom{;}\phantom{;}}\\\phantom{;}5m^{2}+0.9\overline{\smash{)}\phantom{;}125m^{6}\phantom{-;x^n}\phantom{-;x^n}\phantom{-;x^n}\phantom{-;x^n}\phantom{-;x^n}+0.729\phantom{;}\phantom{;}}\\\phantom{\phantom{;}5m^{2}+0.9;}\underline{-125m^{6}\phantom{-;x^n}-22.5m^{4}\phantom{-;x^n}\phantom{-;x^n}\phantom{-;x^n}\phantom{-;x^n}}\\\phantom{-125m^{6}-22.5m^{4};}-22.5m^{4}\phantom{-;x^n}\phantom{-;x^n}\phantom{-;x^n}+0.729\phantom{;}\phantom{;}\\\phantom{\phantom{;}5m^{2}+0.9-;x^n;}\underline{\phantom{;}22.5m^{4}\phantom{-;x^n}+4.05m^{2}\phantom{-;x^n}\phantom{-;x^n}}\\\phantom{;\phantom{;}22.5m^{4}+4.05m^{2}-;x^n;}\phantom{;}4.05m^{2}\phantom{-;x^n}+0.729\phantom{;}\phantom{;}\\\phantom{\phantom{;}5m^{2}+0.9-;x^n-;x^n;}\underline{-4.05m^{2}\phantom{-;x^n}-0.729\phantom{;}\phantom{;}}\\\phantom{;;-4.05m^{2}-0.729\phantom{;}\phantom{;}-;x^n-;x^n;}\\\end{array}$

$25m^{4}-\frac{22.5}{5}m^{2}+\frac{4.05}{5}$