Answer:
(x+4)(x+5)
Step-by-step explanation:
Before we figure out the problem, we must know that the two numbers in the expression must equal the middle number when added and that when multiplied they must equal the last number.
To do this, we list the multiplies of 9 and 20.
9: 1,9,3
20:1,20,2,10,4,5
From there, you go through both lists and follow the given rules stated at the top. When you do that you get, (x+4)(x+5).
To check this answer, you can do a various amount of proofs but the most effective one to me is the F.O.I.L. (first, inner, outer, last) and voila.
