3m+5n-(9-(6m+2n-12n+10m)-m-7m+4n= 9n-8m-(9-6m-2n+12n-10m)=

9n-8m-(9-19m+10n)=9n-8m-9+19m-10n=

11m-n-9

15a^2-(-4a+(5a-8a^2-2a^2+a+9a^2)-3a=

15a^2-(-4a+6a-a^2-3a)= 15a^2-(-a^2-a)=

16a^2+a