Four simple harmonic vibrations 

$\begin{array}{l}{\mathrm{x}}_1=8\sin \left(\mathrm{\omega t}\right),{\mathrm{x}}_2=6\sin \left(\mathrm{\omega t}+\frac{\mathrm{\pi }}{2}\right),\\ {\mathrm{x}}_3=4\sin (\mathrm{\omega t}+\mathrm{\pi })\text{ and }{\mathrm{x}}_4=2\sin \left(\mathrm{\omega t}+\frac{3\mathrm{\pi }}{2}\right)\end{array}$

are superimposed on each other. The resulting amplitude is.... units.