The expression below is the factorization of what trinomial?

(5x + 4)(9x + 9)

a. 45x2 + 81x + 36
b. 14x2 + 13x + 36
c. 45x2 + 13x + 36
d. 14x2 + 81x + 36

The answer is:  [A]:   45x² + 81x + 36 .


Explanation:  Use "FOIL" technique: (First, Outer, Inner, and Last Terms); 
                       then, combine the "like terms", to simplify. 


(5x+4)(9x+9) = 45x² + 45x + 36x + 35 = 45x² + 81x + 36 .
                                                                       (which is answer choice: "A".).