Simplify. All variables represent nonzero real numbers. The power of a power rule
-5y4(y5)2
15y7(y2)3
If you have a power of a power, multiply the two values.
y^5 = y to the fifth power.
Is your first formula = -5y^4 (y^5)^2 ?
If so, it = -5y^4 (y^10) = -5y^14
Now you try it with 15y^7 (y^2)^3 = ?