[tex]\displaystyle 1)\frac{3a+15b}{9ab}=\frac{3(a+5b)}{9ab}=\frac{a+5b}{3ab}[/tex]

[tex]\displaystyle 2) \frac{mn-m}{4(n-1)}=\frac{m(n-1)}{4(n-1)} =\frac{m}{4}[/tex]

[tex]\displaystyle 3) \frac{p^{2}-3p }{4k(p-3)} =\frac{p(p-3)}{4k(p-3)} =\frac{p}{4k}[/tex]

[tex]\displaystyle 4) \frac{xy-2x}{x}=\frac{x(y-2)}{x}=y-2[/tex]

[tex]\displaystyle 5) \frac{m}{m^{2}+mn } =\frac{m}{m(m+n)} =\frac{1}{m+n}[/tex]

[tex]\displaystyle 6) \frac{4a-12c}{7a-21c}=\frac{4(a-3c)}{7(a-3c)} =\frac{4}{7}[/tex]