first off, if it's mixed, you'd want to convert it to "improper" first, and then do the division... say hmm - 3 and 1/7
[tex]\bf \stackrel{mixed}{-3\frac{1}{7}}\implies -\cfrac{3\cdot 7+1}{7}\implies \stackrel{improper}
{-\cfrac{22}{7}}\implies -22\div 7\implies -3.\overline{142857}[/tex]
the line over the decimal part is because is a "recurrent decimal", or repeating one.