Answer:
9 cm
Explanation:
First, we need to find the volume of the cylindrical water bottle. The volume of a cylinder is πr²h where r = radius and h = height. In this case, r = diameter / 2 = 6.5 / 2 = 3.25 and h = 21 so the volume is π * 3.25² * 21 = 221.8125π ≈ 696.84. Let's call the length of the cubic container s. The volume of the cube (which is s³) must be at least the volume of the water bottle, therefore:
s³ ≥ 696.84
∛s³ ≥ ∛696.84
s ≥ 8.86566
The smallest integer value that satisfies this is 9 cm.