[tex]21m^2n=3\cdot\boxed{7}\cdot\boxed{m}\cdot m\cdot\boxed{n}\\\\28mn^2=2\cdot2\cdot\boxed{7}\cdot\boxed{m}\cdot\boxed{n}\cdot n\\\\GCF(21m^2n,\ 28mn^2)=\boxed{7}\cdot\boxed{m}\cdot\boxed{n}=7mn\\-------------------------\\\\\dfrac{21m^2n}{28mn^2}=\dfrac{7mn\cdot 3m}{7mn\cdot4n}=\dfrac{3m}{4n}[/tex]
