6/(m^2-9) =6/(m+3)(m-3)
6/(m^2-9)/2/(m-3)=6/2 *1/(m+3) =3/(m+3)
m/(m+3)-6/(m^2-9)/2/(m-3)
=m/(m+3)-3/(m+3)
=(m-3)/(m+3)