Let's start with the most simple thing: we know that anything to the power of 0 is 1, so we change that. This gives us:
from here, we can see that r^-1 is 1/r, same with the s^-1, and r^-3 is 1/r^3. So, plug that in:
Finaly, we divide.
You should get r^2/qs^3