$\begin{array}{l}\phantom{\phantom{;}x\phantom{;}-3;}{\phantom{;}x^{3}+5x^{2}+15x\phantom{;}+45\phantom{;}\phantom{;}}\\\phantom{;}x\phantom{;}-3\overline{\smash{)}\phantom{;}x^{4}+2x^{3}\phantom{-;x^n}\phantom{-;x^n}-10\phantom{;}\phantom{;}}\\\phantom{\phantom{;}x\phantom{;}-3;}\underline{-x^{4}+3x^{3}\phantom{-;x^n}\phantom{-;x^n}\phantom{-;x^n}}\\\phantom{-x^{4}+3x^{3};}\phantom{;}5x^{3}\phantom{-;x^n}\phantom{-;x^n}-10\phantom{;}\phantom{;}\\\phantom{\phantom{;}x\phantom{;}-3-;x^n;}\underline{-5x^{3}+15x^{2}\phantom{-;x^n}\phantom{-;x^n}}\\\phantom{;-5x^{3}+15x^{2}-;x^n;}\phantom{;}15x^{2}\phantom{-;x^n}-10\phantom{;}\phantom{;}\\\phantom{\phantom{;}x\phantom{;}-3-;x^n-;x^n;}\underline{-15x^{2}+45x\phantom{;}\phantom{-;x^n}}\\\phantom{;;-15x^{2}+45x\phantom{;}-;x^n-;x^n;}\phantom{;}45x\phantom{;}-10\phantom{;}\phantom{;}\\\phantom{\phantom{;}x\phantom{;}-3-;x^n-;x^n-;x^n;}\underline{-45x\phantom{;}+135\phantom{;}\phantom{;}}\\\phantom{;;;-45x\phantom{;}+135\phantom{;}\phantom{;}-;x^n-;x^n-;x^n;}\phantom{;}125\phantom{;}\phantom{;}\\\end{array}$

$x^{3}+5x^{2}+15x+45+\frac{125}{x-3}$