V = 1/3 • π • radius cubed • height
If the volume is is 16π and the height is 3, then 16π = 1/3 • π • r cubed • 3
16π ÷ (1/3 • π • 3) = 16
radius squared = 16 √16 = 4, so radius = 4
You can also check: 1/3 • r cubed • 3 = 16 The only value left to multiply is π