$\begin{array}{l}\phantom{\phantom{;}3x\phantom{;}+1;}{\phantom{;}2x\phantom{;}+1\phantom{;}\phantom{;}}\\\phantom{;}3x\phantom{;}+1\overline{\smash{)}\phantom{;}6x^{2}+5x\phantom{;}-3\phantom{;}\phantom{;}}\\\phantom{\phantom{;}3x\phantom{;}+1;}\underline{-6x^{2}-2x\phantom{;}\phantom{-;x^n}}\\\phantom{-6x^{2}-2x\phantom{;};}\phantom{;}3x\phantom{;}-3\phantom{;}\phantom{;}\\\phantom{\phantom{;}3x\phantom{;}+1-;x^n;}\underline{-3x\phantom{;}-1\phantom{;}\phantom{;}}\\\phantom{;-3x\phantom{;}-1\phantom{;}\phantom{;}-;x^n;}-4\phantom{;}\phantom{;}\\\end{array}$

$2x+1+\frac{-4}{3x+1}$