You could distribute the exponent into the parentheses to both the numerator and denominator of the fraction. For example:
[tex]\frac{4^-^1}{3^-^1} = \frac{\frac{1}{4}}{\frac{1}{3}}}[/tex]
Now multiply the fraction in the numerator by [tex]\frac{3}{3}[/tex] and the fraction in the denominator by [tex]\frac{4}{4}[/tex]
This will yield the fraction [tex]\frac{\frac{3}{12}}{\frac{4}{12}}[/tex]
Finally, multiply both the numerator and denominator by [tex]12[/tex], which will yield the final fraction of [tex]\frac{3}{4}[/tex]
If you plug [tex](\frac{4}{3})^-^1[/tex] into your calculator, you will get the fraction [tex]\frac{3}{4}[/tex]
I hope this helps.