Answer:
x + 4
Step-by-step explanation:
area = length * width
x^2 + 13x + 36 = (x + 9) * width
You need to factor x^2 + 13x + 36.
To factor, you need two numbers that multiply to 36 and add to 13.
The numbers are 9 and 4.
The factorization is:
x^2 + 13x + 36 = (x + 9)(x + 4)
width = x + 4
