Answer

Option C is the correct option
Step by step explanation
Let's find the expression which represents the length of the box:



Write 11x² as a sum

Write 20x as a sum

Factor out x² from the expression

Factor out 12 from the expression

Factor out 32 from the expression

Factor out x+1 from the expression

Factor out 12x as a sum

Reduce the fraction with x-1

Factor out x from the expression

Factor out 4 from the expression

Factor out x+8 from the expression

Reduce the fraction with x+8

hence, x+4 is the expression that represents the length of a box.
Hope I helped!
Best regards!