1)m^2+10m\9-m^2 - 4m-9\9-m^2= 9m^2-m^4+10m+4m+9\9-m^2=9m^2-m^4+14m+9\9-m^2
2)5x-3y\8z + 3x-13y\8z=40xz-3y-3x+13y\8z = 40xz-10y-3x\8z
3)3y+7\4-y + y+15\y-4= 12y-3y^2+7+y+15\4-y= 13y-3y^2+22\4-y
4)(2a-3)^2\9a-27 + ( a-6)^2\27-9a= 4a^2-12a+9+a^2+12a-36\9a-27=5a^2-27\9a-27
5) 25-3x\(x-5)^2 - 7x-x^2\(5-x)^2= 25-3x-7x+x^2\(5-x^2)= 25-10x+x^2\(5-x^2)= (5-x^2)\(5-x^2)= 1