Question 2851
 At first you should know hwo to type 
 A squared minus B squared minus 6B minus 9 as
 A^2 - B^2 -6B - 9

 You only need to use the basic formulas :

 A^2 - B^2 = (A-B)(A+B) ...(1) and 
 (A+B)^2 = A^2 + 2 AB + B^2...(2)

 Now  A^2 - B^2 -6B - 9 =  A^2 - (B^2 +6B + 9)
 = A^2 - (B+3)^2  [Use formula (2), why?]
 = [(A+(B+3)][A-(B+3)] [Use formula (2)]
 = (A+B+3)(A-B-3)

 That is the whle story.
 Something if you suppose it is hard  then it becomes more
 difficult.However,if youthink it is easy, it becomes facile.
 Math is not hard at all if you have basic confidence aboutyourself.
 
 Normally, don't anwser such simple questions as you asked.
 Here,I just don't want you see other long troublesome answers and 
 I don't want you give up.

 Kenny