$\begin{array}{l}\phantom{\phantom{;}4a\phantom{;}+3;}{\phantom{;}3a^{2}-3a\phantom{;}+1\phantom{;}\phantom{;}}\\\phantom{;}4a\phantom{;}+3\overline{\smash{)}\phantom{;}12a^{3}-3a^{2}-5a\phantom{;}+10\phantom{;}\phantom{;}}\\\phantom{\phantom{;}4a\phantom{;}+3;}\underline{-12a^{3}-9a^{2}\phantom{-;x^n}\phantom{-;x^n}}\\\phantom{-12a^{3}-9a^{2};}-12a^{2}-5a\phantom{;}+10\phantom{;}\phantom{;}\\\phantom{\phantom{;}4a\phantom{;}+3-;x^n;}\underline{\phantom{;}12a^{2}+9a\phantom{;}\phantom{-;x^n}}\\\phantom{;\phantom{;}12a^{2}+9a\phantom{;}-;x^n;}\phantom{;}4a\phantom{;}+10\phantom{;}\phantom{;}\\\phantom{\phantom{;}4a\phantom{;}+3-;x^n-;x^n;}\underline{-4a\phantom{;}-3\phantom{;}\phantom{;}}\\\phantom{;;-4a\phantom{;}-3\phantom{;}\phantom{;}-;x^n-;x^n;}\phantom{;}7\phantom{;}\phantom{;}\\\end{array}$

$3a^{2}-3a+1+\frac{7}{4a+3}$