4/(a2+12a+27)=4/((a+9)(a+3)); 5/(a2+10a+21)=5/((a+7)(a+3)).
So sum is:
4/((a+9)(a+3))+5/((a+7)(a+3))=(1/(a+3))(4/(a+9)+5/(a+7))=
(1/(a+3))(4a+28+5a+45)/((a+7)(a+9))=
(1/(a+3))(9a+73)/(a2+16a+63)=
(9a+73)/(a3+16a2+63a+3a2+48a+189)=(9a+73)/(a3+19a2+111a+189).
Could also be written (9a+73)/((a+3)(a+7)(a+9)).