Answer: 25.12 cm
Here the measure of the arc is \(80^\circ\) (the "cm" in the question is a misprint: an arc's measure is an angle).
Area of sector \(=\dfrac{\theta}{360}\times\pi r^2\); length of arc \(=\dfrac{\theta}{360}\times2\pi r\).
\[l=\frac{80}{360}\times2\times3.14\times18=\frac29\times113.04\]
\[=25.12\ \text{cm}\]