When dividing exponents, it is just subtraction. The -y is actually -y^1. Since the numerator has the same variable and nothing is being multiplied or divided in it, we can just subtract 1 from each exponent.
-5y^5 would just be -5y^4 and 7y^4 would become 7y^3.
Now the denominator is not gone. The y is gone, but there is still a -1 there. All this means is you need to switch the signs up top. The final simplified solution would be