d
(d) The given equation can be written as
$y = 4\sin \,\left( {4\pi t - \frac{{\pi x}}{{16}}} \right)$ $(v) = \frac{{{\rm{Co - efficient of}}\,t(\omega )}}{{{\rm{Co - efficient of}}\,x(K)}}$
==> $v = \frac{{4\pi }}{{\pi /16}} = 64\,cm/sec$ along $+x$ direction.