Answer:
The height of the box is:
4 ft.
Explanation:
Let "h" denotes the height of the box.
Length of box is denoted by "l"
and breadth or width of box is denoted by "b"
We are given l=18 ft
b=8 ft.
Also we are given surface area of rectangular box= 496 ft²
As we know that the surface area of box is given by:

i.e.

Divide both side by 2.

on dividing both side by 26 we get:

Hence, the height of the box is:
4 ft.