The rule goes that if you have any value (whether a fraction or not) raised to a negative exponent, you take its reciprocal.
Meaning, (5/6)^-1 will can simply be written as 6/5. We just flip it around.
With whole numbers, we can also think of them as fractions with their denominators being 1. For instance, 3 can be thought of as 3/1, so 3^-1 would be written as 1/3!
Hope that helps :)