Letters in the Lengths

A length can be given as an expression, like x + 2. The formula still works: put the expression in where the length goes, and solve for x.

This cylinder has radius 3, height x + 2 and volume 63π. The rule gives $63 = {3}^{2}\cdot \left(x+2\right)$ once π is divided out, so $7 = x+2$ and $x = 5$. The height is 7.

Read the question to the end: sometimes it asks for x, sometimes for the length itself. Here x is 5 and the height is 7.