Three waves of equal frequencies having amplitudes $10\mathrm{\mu m},4\mathrm{\mu m}\mathrm{and}7\mathrm{\mu m}$ arrive of a given point. Phase difference between first and second wave is $\frac{\mathrm{\pi }}{2}$ and that between second and third wave is $\frac{\mathrm{\pi }}{2}.$ .Then amplitude of the resulting wave in $\mathrm{\mu m}$ ,is