Answer:
[tex]m^{21}[/tex]
Step-by-step explanation:
[tex](\frac{m^{13} }{m^{20}})^{-3} = (\frac{1}{m^7})^{-3}=(m^{-7})^{-3}=m^{(-7)*(-3)}=m^{21}[/tex]
