1. V = s3
2. V = pr2h
3. V = Bh
Joint variation means that V will be dependent on at least two different variables. Looking at the three choices, only 2 and 3 show this.
In 2, V varies jointly as r2 and h (assuming p is the constant of proportionality). And in 3, V varies jointly as B and h, with the proportionality constant being 1.
