Only height, because when you have an expression that relies only on multiplication (not addition or subtraction), we'll say:
cb = a
Tripling either c or b will also triple a. For example:
(8)(3) = 24
(8 + 8 + 8)(3) = 24(3)
(24)(3) = 24(3)
This will be true even if you multiply c by any other number.
So, in the expression v = πr²h, any term except r can be tripled with the result of tripling v. We exclude r because r has an exponent, which means tripling r will more than triple v.