We just have to flip the fraction to transform the exponent into a positive
[tex](\frac{11}{7})^{-3}=(\frac{7}{11})^3[/tex]
Then, we use the power of a division property
[tex]\frac{7^3}{11^3}=\frac{7\times7\times7}{11\times11\times11}=\frac{343}{1331}[/tex]
Hence, the first power is equal to 343/1331.
We use the same properties for the second power
[tex](-\frac{5}{r})^{-3}=(-\frac{r}{5})^3=-\frac{r\times r\times r}{5\times5\times5}=-\frac{r^3}{125}[/tex]
