Answer:
The length of the box is (x+4).
Explanation:
The volume of a rectangular prism is represented by the function

Rewrite the given function in factored form.

It is given that the width of the box is x – 1 while the height is x + 8.
The volume of a rectangular prism is

where, l is length, b is width and h is height.
Divide both sides by bh.

Substitute the value of volume, height and width.

Cancel out the common factors.

Therefore the length of the box is (x+4).