THE POWER OF A POWER RULE:
__-5Y^4(Y^5)^2__
15Y^7(Y^2)^3
-5Y^4 * Y^10/15Y^7 * Y^6
When you multiply exponents, you add them
-5Y^14/15Y^12
When dividing exponents, you substract from the top and bottom
I think the final answer would be
-y^2/3