[tex]\frac{4n-m}{20mn^{2}} \frac{3m+n}{15^{2}n} \\\\\frac{b+3}{9b-27} - \frac{b-1}{b^{2}-3b}\\\\\frac{m^{2}-10mn+25n^{2}}{12m^{3}n^{2}} / \frac{m-5n}{6mn}\\\\\frac{a+3}{1-a} * (\frac{a}{a-3} + \frac{3-a}{a+3})[/tex]