When you raise something to the power of -1, all that happens is that thing turns upside down.
For example: (x^3 / y^4)^-1 will become (y^4 / y^3), basically the same fraction but just swap the numerator and denominator.
In your example, the first exponent is 4 and the second exponent is 3.
Answer: y^4 and x^3
