8. Calculate the arc length (to the nearest tenth of a metre) of a sector of a circle with radius $8.4 \mathrm{~m}$ if the sector angle is $80^{\circ}$.

Step 1 ：We are given a sector of a circle with radius \(r = 8.4\) m and sector angle \(\theta = 80^\circ\).

Step 2 ：We can calculate the arc length of the sector using the formula: Arc length = \(\frac{\theta}{360} \times 2\pi r\).

Step 3 ：Substituting the given values into the formula, we get: Arc length = \(\frac{80}{360} \times 2\pi \times 8.4\).

Step 4 ：Solving the above expression, we find that the arc length is approximately 11.7 m.

Step 5 ：Final Answer: The arc length of the sector of the circle is \(\boxed{11.7}\) metres.