(Velocity of sound in air $=333 \mathrm{~m} / \mathrm{s}$ )
$\mathrm{f}=\frac{\mathrm{nv}}{2 \mathrm{~L}}$
$\Delta \mathrm{f}=\frac{6 \mathrm{v}}{2 \times 0.6}-\frac{5 \mathrm{v}}{2 \times 0.9}$
$\mathrm{v}=333 \mathrm{~m} / \mathrm{s}$
$\Delta \mathrm{f}=740 \mathrm{~Hz}$
$Y = A\sin (100t)\cos (0.01x)$
where $Y$ and $A$ are in millimetre, $t$ is in seconds and $x$ is in metre. The velocity of wave is ..... $m/s$