A transverse wave propagating along x-axis is represented by $Y(x,t)=8.0 \sin (0.5 \pi x-4\pi-\frac {\pi }{4})$ where x is in metres and t is in seconds. The speed of the wave is:-

Question

( A ) $4m/s$
( B ) $8m/s$
( C ) $\frac {\pi}{4}m/s$
( D ) $0.5m/s$