What is the formula for finding the height of a cylinder?

That depends on what you already know about it. Formulas are just relationships between what you do know and what you don't know. I can't tell you what formula to use until you tell me what you know.

Example:

If you know the volume of the cylinder and its radius, then Height = Volume / pi xradius2

If you know the area of the cylinder and its radius, then Height = Area / 2 x pi x Radius

If you know the volume and area of the cylinder, then Height = Area2 / 4 x pi x Volume