Find the exact length of the arc made by the central angle theta equals 22 degrees in a circle of radius r equals 18 ⁢ μm.

Arc length = (22/360) * 2pi*r

$${\frac{{\mathtt{22}}}{{\mathtt{230}}}}{\mathtt{\,\times\,}}{\mathtt{2}}{\mathtt{\,\times\,}}{\mathtt{\pi}}{\mathtt{\,\times\,}}{\mathtt{18}} = {\mathtt{10.818\: \!006\: \!007\: \!143\: \!983\: \!7}}$$

Oh you wanted the exact length  :/

22 degrees = 22*pi/180 radians

     $$\\Arc\;\;length\\\\ =\frac{22\pi}{180}*2*\pi*18\\\\ =\left[\frac{22\pi}{180}\div (2\pi)\right]*2*\pi*18\\\\ =\left[\frac{22\pi}{180}\times \frac{1}{ (2\pi)}\right]*2*\pi*18\\\\ =\left[\frac{11}{180}\right]*2*\pi*18\\\\ =\frac{11\pi}{5}\;\micro \mu m\\$$