b
(b) From the given equation amplitude $a = 0.04m$
Frequency $ = \frac{{{\rm{Co}} - {\rm{efficient of t}}}}{{2\pi }}$
$ = \frac{{\pi /5}}{{2\pi }} = \frac{1}{{10}}Hz$
Wave length $\lambda = \frac{{2\pi }}{{{\rm{Co}} - {\rm{efficient}}\;of\;x}}$
$ = \frac{{2\pi }}{{\pi /9}}=18m.$
Wave speed $v = \frac{{{\rm{Co - efficient of }}t}}{{{\rm{Co - efficient of }}x}}$
$ = \frac{{\pi /5}}{{\pi /9}} = 1.8m/s.$