let's firstly convert the mixed fractions to improper fractions, then divide.
[tex]\bf \stackrel{mixed}{3\frac{1}{10}}\implies \cfrac{3\cdot 10+1}{10}\implies \stackrel{improper}{\cfrac{31}{10}} \\\\[-0.35em] ~\dotfill\\\\ \cfrac{2}{5}\div \cfrac{31}{10}\implies \cfrac{2}{~~\begin{matrix} 5 \\[-0.7em]\cline{1-1}\\[-5pt]\end{matrix}~~}\cdot \cfrac{\stackrel{2}{~~\begin{matrix} 10 \\[-0.7em]\cline{1-1}\\[-5pt]\end{matrix}~~}}{31}\implies \cfrac{4}{31}[/tex]
