Your answer would be 27.
This is because the formula for the volume of a cylinder is πr² × h, and the formula for a cone is 1/3 × (πr² × h), which we can also write as (πr² × h)/3.
This means that a cone that fits perfectly inside a cylinder will have a volume that is 1/3 the volume of the cylinder. Thus, 81 ÷ 3 = 27.
I hope this helps!