[填空题]
The diagram below shows a sectmbzf6*x8w*ee;, myr .,u hnt aor of a circle with radius re4z /n762gk fl(d8edmr2lv, /jplgh m where $\mathrm{AO} \hat{\mathrm{B}}=x $ radians and the length of the $\operatorname{arc}$ A B is $\frac{4}{x} \mathrm{~cm}$ .
$\text { Given that the area of the sector is } 27 \mathrm{~cm}^{2} \text {, find the length of the arc } A B \text {. }$
