(81-a²)/(a²+6a+9)÷(a-9)/(2a+6)+(a+15)/(a+3)
=(9+a)(9-a)/(a+3)²÷(a-9)/(2a+6)+(a+15)/(a+3)
=-(9+a)(2a+6)/(a+3)²+(a+15)/(a+3)
=(-18a-54-2a²+6a+a²+18a+45)/(a+3)²
=(-a²+6a-9)/(a+3)²
=-(a-3)²/(a+3)²