JAMB 2015 · UTME · Q11

A solid cylinder of radius $3\text{ cm}$ has a total surface area of $36\pi\text{ cm}^2$ . Find its height.

Worked solution (try it first)

Total surface area of a solid cylinder: $2\pi r(r + h) = 2\pi \times 3 \times (3 + h)$
$= 6\pi(3 + h)$ .
Set it equal to $36\pi$ and divide both sides by $6\pi$ : $3 + h = 6$ .
So $h = 3$ cm, option B.