Answer:
The box is 7.5 in long.
Explanation:
Calculate the total surface area of the sides of this box (neglecting the ends).
If the base is 3" by 3" and the length of the box is 6", then the total surface area (without ends) is 4 times 3" by x, or 12x in². 80% of this "lateral surface area" is 0.80(12x in²), or 9.60x in° and this 9.60x in² represents the surface area covered b y the label. That label surface area is 4(3 in by 6 in), or 72 in²
Equating 9.60x in² and 72 in² and solving for x yields x = (72 in²) / (9.60 in²:
x = 7.5 in
The box is 7.5 in long.