The expression would be 1/9
To do this in the simplest way possible, start by subtracting the exponents since they are being divided.
-6 - (-4) = -2.
So the end result is 3^-2. This can be easily expressed by moving the term to the denominator and making it positive. Like this:
Then we can eliminate the exponent, leaving us with:
This is a division so the exponents are subtracted:
3^-6 / 3 ^-4