Answer:
[tex]-8y^{25}\\-9y^6\\5y^5[/tex]
Step-by-step explanation:
First one.
[tex]((-y)^5)(8y^{20})=-y^5*8y^{20}=-8y^{5+20}=-8y^{25}[/tex]
Second one
[tex]((-y)^{5} )(9y)=-y^5*9y=-9y^{5+1}=-9y^6[/tex]
and last one
[tex]((-y)^5)(-5)=-y^5*(-5)=5y^5[/tex]