5x^-1/-y^-1

once again, what are you asking?

how is this simplified

-y/5x

Whenever you have anything raised to the negative power, flip it upside down. So:

X^-1 = 1/X
or
X^-3 = 1/(X^3)

Whenever anything is raised to the 1 power, it is itself.

X^1 = X
12398719283719^1 = 12398719283719

Whenever anything is raised to the 0 power, it is 1.

X^0 = 1
12398719283719^0 = 1