$\begin{array}{l}\phantom{\phantom{;}3x\phantom{;}-5;}{\phantom{;}12x^{3}+20x^{2}-3x\phantom{;}-5\phantom{;}\phantom{;}}\\\phantom{;}3x\phantom{;}-5\overline{\smash{)}\phantom{;}36x^{4}\phantom{-;x^n}-109x^{2}\phantom{-;x^n}+25\phantom{;}\phantom{;}}\\\phantom{\phantom{;}3x\phantom{;}-5;}\underline{-36x^{4}+60x^{3}\phantom{-;x^n}\phantom{-;x^n}\phantom{-;x^n}}\\\phantom{-36x^{4}+60x^{3};}\phantom{;}60x^{3}-109x^{2}\phantom{-;x^n}+25\phantom{;}\phantom{;}\\\phantom{\phantom{;}3x\phantom{;}-5-;x^n;}\underline{-60x^{3}+100x^{2}\phantom{-;x^n}\phantom{-;x^n}}\\\phantom{;-60x^{3}+100x^{2}-;x^n;}-9x^{2}\phantom{-;x^n}+25\phantom{;}\phantom{;}\\\phantom{\phantom{;}3x\phantom{;}-5-;x^n-;x^n;}\underline{\phantom{;}9x^{2}-15x\phantom{;}\phantom{-;x^n}}\\\phantom{;;\phantom{;}9x^{2}-15x\phantom{;}-;x^n-;x^n;}-15x\phantom{;}+25\phantom{;}\phantom{;}\\\phantom{\phantom{;}3x\phantom{;}-5-;x^n-;x^n-;x^n;}\underline{\phantom{;}15x\phantom{;}-25\phantom{;}\phantom{;}}\\\phantom{;;;\phantom{;}15x\phantom{;}-25\phantom{;}\phantom{;}-;x^n-;x^n-;x^n;}\\\end{array}$

$12x^{3}+20x^{2}-3x-5$