d
(d) Standard wave equation which travel in negative $x-$ direction is $y = A\sin (\omega \,t + kx + {\varphi _0})$
For the given wave $\omega = 2\pi n = 15\pi ,\,\,k = \frac{{2\pi }}{\lambda } = 10\pi $
Now $v = \frac{{{\rm{Co - efficient \,of\, }}t}}{{{\rm{Co - efficient \,of \,}}x}}$ $ = \frac{\omega }{k} = \frac{{15\pi }}{{10\pi }} = 1.5\,m/sec$
and $\lambda = \frac{{2\pi }}{k} = \frac{{2\pi }}{{10\pi }} = 0.2\,m.$