What additional piece of information must be known in order to calculate the volume of the cylinder below?

Your question is missing a diagram, therefore, I cannot provide an exact answer.
However, I can help you with the concept.

The volume of the cylinder can be calculated as follows:
volume of cylinder = πr²h
where:
π is a constant = 3.14
r is the radius of the cylinder
h is the height of the cylinder

Therefore, to be able to calculate the volume, we need to know both the radius and the height of the cylinder or have a relation between the two

Examples:
1- given that the height of the cylinder is 12 cm and that the radius is 3 cm:
volume = 3.14*(3)²*(12) = 339.12 cm³

2- given that the radius of the cylinder is 4 cm and that the height is twice the radius:
height = 2*radius = 2*4 = 8 cm
volume = 3.14*(4)²*(8) = 401.92 cm³

3- given that the height of the cylinder is 16 and that the radius of the cylinder is 1/4 of the height
radius = 1/4 * 16 = 4 cm
volume = 3.14*(4)²*16 = 803.84 cm³

Hope this helps :)

Ibelieve 4mn because it’s like you’re combining them